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Full text of "The vertebrate skeleton"

Cambrfrg* Natural g>titntt iHanualsf 

BIOLOGICAL SERIES. 
GENERAL EDITOR : ARTHUR E. SHIPLEY, M.A. 

FELLOW AXD TUTOR OF CHRISTS COLLEGE, CAMBRIDGE. 



THE 

VEKTEBKATE SKELETON, 



C. J. CLAY AND SONS, 
CAMBRIDGE UNIVERSITY PRESS WAREHOUSE, 

AVE MARIA LANE. 

laagofo: 263, ARGYLE STREET. 

AND 

H. K. LEWIS, 
136, GOWEE STREET, W.C. 




ILtipng: F. A. BROCKHAUS. 

efo iork: THE MACMILLAN CO. 

Bombag: GEORGE BELL AND SONS. 




THE 

VEETEBRATE SKELETON 



BY 



SIDNEY H. REYNOLDS, M.A., 

TRINITY COLLEGE, CAMBRIDGE ; 

LECTUBKB AXD DEMONSTRATOR IX GEOLOGY AXD ZOOLOGY AT UNIVKB8ITT 
COLLEGE, BRISTOL. 




CambuliQt : 
AT THE UNIVERSITY PRESS, 

1897 
[All Rights reserved.} 



Cambridge : 

PRINTED BY J. & C. Y. CLAY, 
AT THE UNIVERSITY PRESS. 



" 



v* 



PREFACE. 



IN the following pages the term skeleton is used in its 
widest sense, so as to include exoskeletal or tegumentary 
structures, as well as endoskeletal structures. It was thought 
advisable to include some account of the skeleton of the 
lowest Chordata animals which are not strictly vertebrates, 
but it seemed undesirable to alter the title of the book in 
consequence. 

The plan adopted in the treatment of each 'group has 
been to give first an account of the general skeletal characters 
of the group in question and of its several subdivisions : 
secondly to describe in detail the skeleton of one or more 
selected types : and thirdly to treat the skeleton as developed 
in the group organ by organ. 

A beginner is advised to commence, not with the intro- 
ductory chapter, but with the skeleton of the Dogfish, then 
to pass to the skeletons of the Newt and Frog, and then 
to that of the Dog. After that he might pass to the intro- 
ductory chapter and work straight through the book. I have 
endeavoured to make the account of each type skeleton 
complete in itself : this has necessitated a certain amount of 



VI PREFACE. 

repetition, a fault that I have found it equally difficult to 
avoid in other parts of the book. 

Throughout the book generic names are printed in italics ; 
and italics are used in the accounts of the type skeletons for 
the names of membrane bones. Clarendon type is used to 
emphasise certain words. In the classificatory table the 
names of extinct genera only, are printed in italics. 

In a book in which an attempt is made to cover to some 
extent such a vast field, it would be vain to hope to have 
avoided many errors both of omission and commission, and 
I owe it to the kindness of several friends that the errors are 
not much more numerous. I cannot however too emphatically 
say that for those which remain I alone am responsible. 
Messrs C. W. Andrews, E. Fawcett, S. F. Harmer, J. Graham 
Kerr, and B. Rogers have all been kind enough to help me 
by reading proofs or manuscript, while the assistance that I 
have received from Dr Gadow during the earlier stages and 
from Prof. Lloyd Morgan and Mr Shipley throughout the 
whole progress of the work has been very great. To all these 
gentlemen my best thanks are tendered. 

All the figures except 1, 35, 55, and 84 were drawn by 
Mi 1 Edwin Wilson, to whose care and skill I am much in- 
debted. The majority are from photographs taken by my 
sister Miss K. M. Reynolds or by myself in the British 
Museum and in the Cambridge University Museum of 
Zoology, and I take this opportunity of thanking Sir W. H. 
Flower and Mr S. F. Harmer for the facilities they have 
afforded and for permission to figure many objects in the 
museums respectively under their charge. I have also to 
thank (1) Prof, von Zittel for permission to reproduce figs. 27, 
41, 52, 69, 70, 80, 106 A, and 107 c; (2) Sir W. H. Flower 
and Messrs A. and C. Black for figs. 1 and 84; (3) Prof. O. C. 



PREFACE. Vll 

Marsh and Dr H. Woodward for fig. 35 ; (4) Dr C. H. Hurst 
and Messrs Smith, Elder, and Co. for tig. 55. 

A few references are given, but no attempt has been made 
to give anything like a complete list. The abbreviations 
of the titles of periodicals are those used in the Zoological 
Record. 

I have always referred freely to the textbooks treating of 
the subjects dealt with, and in particular I should like to 
mention that the section devoted to the skeleton of mammals 
is, as it could hardly fail to be, to a considerable extent based 
on Sir W. H. Flower's Osteology of the Mammalia. 

SIDNEY H. REYNOLDS. 

March 10, 1897- 



CONTENTS. 



CHAPTER I. 

PAGE 

Introductory account of the skeleton in general .... 1 

CHAPTER II. 

Classification 30 

CHAPTER III. 
Skeleton of Hemichordata. Urochordata and Cephalochordata . 50 

CHAPTER IV. 

Skeletal characters of the Vertebrata. The skeleton in the Cyclo- 

stomata ........... 53 

CHAPTER V. 

Skeletal characters of the Ichthyopsida. Characters of the several 

groups of Pisces 59 

CHAPTER VI. 
The skeleton of the Dogfish (Scy Ilium canicula) .... 71 



X CONTENTS. 

CHAPTER VII. 

PAGE 

The skeleton of the Codfish (Gadua morrhua) and the skull of 

....... 83 



CHAPTER VIII. 

General account of the skeleton in Fishes ..... 104 / 

CHAPTER IX. 

i 

Characters of the several groups of Amphibia .... 133 

CHAPTER X. 

The skeleton of the Newt (Molge cristata) ..... 138 ~" 

CHAPTER XI. 

The skeleton of the Frog (Rana temporaria) .... 151 

CHAPTER XII. 

General account of the skeleton in Amphibia . . . . 168 

CHAPTER XIII. 

Skeletal characters of the Sauropsida. Characters of the several 

groups of Eeptiles ......... 189 

CHAPTER XIV. 

The skeleton of the Green Turtle (Chelone midas) . . . 214 

CHAPTER XV. 

The skeleton of the Crocodile (Crocodilus palustris) . . . 237 * 

CHAPTER XVI. 

General account of the skeleton in Beptiles ..... 270 



CONTENTS. XI 

CHAPTER XVII. 

PAGE 

Characters of the several groups of Birds 295 

CHAPTER XVIII. 

The skeleton of the Wild Duck (Anas boschas) .... 302 

CHAPTER XIX. 


General account of the skeleton in Birds 328 

CHAPTER XX. 

Characters of the several groups of Mammalia .... 343 

CHAPTER XXI. 

The skeleton of the Dog (Cam* familiaris) 374 

CHAPTER XXII. 

General account of the skeleton in Mammalia. The exoskeleton 

and vertebral column 416 

CHAPTER XXIII. 

General account of the skeleton in Mammalia (continued). The 

skull and appendicular skeleton 455 



LIST OF ILLUSTRATIONS. 



FIG. PAGE 

1 Diagrammatic sections of various forms of teeth ... 6 

> 2 Cervical vertebrae of an Ox (Bos taurus) .... 15 

3 Diagram of the skeleton of Amphioxus lanceolatus . . 51 

4 Dorsal, lateral, and ventral views of the skull of Petro- 

myzon marinns ......... 56 

5 Skull of a male Chimaera monstrosa 65 

6 Lateral view of the skull of a Dogfish (Scy Ilium canicula) . 75 

7 Semidorsal view of the pectoral girdle and fins of a Dogfish 

(Scyllium canicula) ........ 80 

8 Dorsal view of the pelvic girdle and fins of a male Dogfish 

(Scyllium canicula) 81 

9 Dorsal and ventral views of the cranium of a Salmon (Salwo 

solar) from which most of the membrane bones have been 

removed 88 

10 Lateral view of the chondrocranium of a Salmon (Salnto 

salar) 90 

11 Lateral view of the skull of a Salmon (Salmo salar) . . 92 

12 Mandibular and hyoid arches of a Cod (Gadus morrhua) . 99 

13 Right half of the pectoral girdle and right pectoral fin of a Cod 

(Gadus morrhua) 102 

14 Diagram of a section through the jaw of a Shark (Odontaxpi* 

americanus) showing the succession of teeth . . . 107 

15 Part of the lower jaw of a Shark (Galeus) .... 108 

16 Skulls of Notidanus and Cestracion ..... 118 

17 Dorsal view of the branchial arches of Heptanchus . . 120 

18 Lateral view of the skull of a Sturgeon (Acipenser sturio) . 122 

19 Dorsal and ventral views of the cranium of Ceratodus miolepix 125 

20 Lateral view of the skeleton of Ceratodus miolepis . . 128 

21 Dorsal, ventral and lateral views of the skull of a Newt (Molge 

cristata) 142 

22 Ventral and lateral views of the shoulder-girdle and sternum 

of an old male Crested Newt (Molge cristata) . . . 146 



LIST OF ILLUSTRATIONS. Xlll 



FIG. 

23 Eight posterior and anterior limbs of a Newt (Molge 

cristata) .......... 148 

24 Dorsal and ventral views of the cranium of a Common Frog 

(Rana temporarid) ........ 155 

2-5 Dorsal and ventral views of the cranium of a Common Frog 
(Rana temporaria) from which the membrane bones have 
mostly been removed ........ 157 

26 Lateral view of the skull and posterior view of the cranium of 

a Common Frog (Rana temporaria) ..... 159 

27 Dorsal view of the skull of a Labyrinthodont (Capitosaurus 

namtus) .......... 176 

28 Ventral view of the cranium, and lateral view of the cranium 

and mandible of Siphonops anmtlatus .... 178 

29 Visceral arches of Amphibia : A, Jlolge cristata ; B, Rana 

temporaria, adult ; C, Tadpole of Rana ; D, Siredon pisci- 
formis ........... 181 

30 Shoulder-girdle and sternum of an adult male Common Frog 

(Rana temporaria), and of an adult female Docidophryne 
gigantea .......... 183 

31 A, Right antibrachium and manus of a larval Salamander 

(Salamandra maculosa); B, Bight tarsus and adjoining 
bones of Molge sp ........ v . 186 

32 Lateral and dorsal views of the skull of an Ichthyosaurus . 196 

33 Lateral view and longitudinal section of the skull of a Lizard 

(Varanus varius) ......... 201 

34 Lateral view cf the shoulder-girdle of a Lizard (Varanus) . 202 

35 Bestored skeleton of Ceratosaurus nasicornis . . . 206 

36 Dorsal and ventral views of the carapace of a Loggerhead 

Turtle (Thalassochelys caretta) ...... 216 

37 Plastron of a Green Turtle (Chelone midas) . . . .218 

38 The skull of a Green Turtle (Chelone midas) ... 223 

39 Longitudinal vertical section through the cranium of a Green 

Turtle (Chelone midas) ....... 226 

40 Anterior limb of a young Hawksbill Turtle (Chelone imbri- 

cata), and posterior limb of a large Green Turtle (Chelone 
midas) ........... 234 

. 41 The first four cervical vertebrae of a Crocodile (Crocodilus 

vulgaris) .......... 239 

J 42 Anterior view of a late thoracic and the first sacral vertebrae 

of a Crocodile (Crocodilus palustris) ..... 242 



XIV LIST OF ILLUSTRATIONS. 

FIG. PAGE 

43 Palatal aspect of the cranium and mandible of an Alligator 

(Caiman latirostris) . . 245 

44 Lateral view of the skull of an Alligator (Caiman latirostris) . 248 

45 Longitudinal section through the skull of an Alligator (Caiman 

latirostris) 253 

46 Sternum and associated membrane bones of a Crocodile 

(Crocodilus palustris) . . . . . . . . 261 

47 Left half of the pectoral girdle of an Alligator (Caiman 

latirostris) 262 

48 Bight anterior and posterior limbs of an Alligator (Caiman 

latirostris) .......... 264 

49 Pelvis and sacrum of an Alligator (Caiman latirostris) . 267 

50 Preparation of part of the right mandibular ramus of Croco- 

dilus palustris 274 

51 Dorsal and ventral views of the skull of a Common Snake 

(Tropidonotus natrix) . . 279 

52 Skull of Hatteria (Sphenodon punctatus) .... 282 

53 Hyoids of an Alligator (Caiman latirostris), and of a Green 

Turtle (Chelone midas) 285 

54 Ventral view of the shoulder-girdle and sternum of Loemanctiis 

longipes 287 

55 Left half of the skeleton of a Common Fowl (Gallus bankiva) 301 

56 The wing of a Wild Duck (Anas boschas) .... 304 

57 Wings of a Wild Duck with the coverts removed (An<ts 

boschas) 305 

58 Dorsal and ventral views of the pelvis and sacrum of a Duck 

(Anas boschas) 311 

59 Skull of a Duck (Anas bosclias) 312 

60 A, Ventral view of the cranium of a Duck (Anas boschas) ; B, 

Cranium and mandible seen from the left side . . 313 

" 61 Lateral view of the pelvis and sacrum of a Duck (Anas boschas) 325 

62 Third cervical vertebra of an Ostrich (Struthio camelus) . 331 

63 Shoulder-girdle and sternum of A, Black Vulture (Vultur 

cinereus) ; B, Peacock (Pavo cristatus) ; C, Pelican (Pelica- 

nus conspicillatus) 337 

64 Bones of the right wing of A, a Penguin; B, an Ostrich 

(Struthio camelus) and C, a Gannet (Sula alba) . . . 339 

65 Pelvic girdle and sacrum of A, Cassowary (Casuarius galeatus) ; 

B, Owen's Apteryx (A. oweni); C, Broad-billed Ehea (R. 
macrorhyncha) ; D, Ostrich (Struthio camelus) . . . 340 



LIST OF ILLUSTRATIONS. XV 

FIG. PAGE 

66 Ventral view of the shoulder-girdle and sternum of a Duckbill 

(Ornithorhynchus paradoxus) 347 

67 Cervical vertebrae of a Ca'ing Whale (Globicephalus melas) . 354 

68 Dentition of a Dog (Canis familiaris) 375 

- 69 Atlas and axis vertebrae of a Dog (Canis familiaris) . . 379 

- 70 Second thoracic and second lumbar vertebrae of a Dog (Cam's 

familiaris) 382 

71 Diagram of the relations of the principal bones in the Mamma- 

lian skull 385 

72 Vertical longitudinal section through skull of a Dog (Canis 

familiaris) 387 

73 Dorsal view of the cranium of a Dog (Canis familiaris) . . 389 

74 Diagram of the mammalian tympanic cavity and associated 

bones 391 

75 Ventral view of the cranium of a Dog (Canis familiaris) . . 396 

76 Sternum and sternal ribs of a Dog (Cam's familiaris) . . 403 

77 Bones of the left upper arm and fore-arm of a Dog (Canis 

familiaris) .......... 407 

78 Bight innominate bone, A, of a full-grown Terrier: B, of a 

Collie Puppy 

79 Left leg bones of a Dog (Canis familiaris) .... 

80 A, Eight manus ; B, Right pes of a Dog (Canis famili- 

aris) 413 

81 Skull of a young Indian Rhinoceros (P. unicornis) showing the 

change of the dentition " . 421 

82 Palatal aspect of the cranium and mandible of a Donkey (Equus 

asinus) .......... 431 

83 Sknll of Procavia (Dendrohyrax) dorsalis .... 433 

84 Carnassial or sectorial teeth of Carnivora .... 436 

85 Mandible of Isabelline Bear (Ursus isabellinus) . . . 438 

86 Left mandibular ramus of the Sea Leopard (Ogmorhinus 

leptanyx) 439 

- 87 Cervical vertebrae of a young Fin Whale (Balaenoptera 
musculus) ......... 

88 Atlas and axis vertebrae of an Ox (Bos taunts) . 

89 First and second thoracic vertebrae of an Ox (Bos taurus) 

90 Skulls of Tasmanian Wolf (Thylacinus cynocephalus) and 

Hairy-nosed Wombat (Phascolomys latifrons) . . . 456 

91 Skull of Two-fingered Sloth (Choloepus didactyltis) . . 458 

92 Skull of Rhytina stelleri 460 



XVI LIST OF ILLUSTRATIONS. 

FIG. PAGE 

93 Lateral view and longitudinal section of the skull of a young 

Ca'ing Whale (Globicephalus melas) ..... 463 

94 Cranium and mandible of a Pig (Sus scrofa) . . . 466 

95 Mandible of a Hippopotamus (Hippopotamus amphibius) . 467 

96 Skull of a young Indian Elephant (Elephas indicus) . . 474 

97 Longitudinal section of the skull of a young Indian Elephant 

(Elephas indicus) 475 

98 Half-front view of the skull of a Porcupine (Hystrix cristata) . 477 

99 Skulls of an old and of a young Gorilla (Gorilla savagei) . 483 

100 Malleus, stapes, and incus of Man, Dog, and Rabbit . . 485 

101 Skeleton of a Cape Buffalo (Bubalus caffer) .... 492 

102 Lateral and dorsal views of the shoulder-girdle and part of 

the sternum of the Spiny Anteater (Echidna aculeata) . 494 

103 Skeleton of a Llama (Auchenia glama) .... 496 

104 Dorsal view of the sternum and right half of the shoulder- 

girdle of Mus sylvaticus 498 

105 Anterior surface of the right humerus of a Wombat (Phasco- 

lomys latifrons) 500 

106 Manus of Perissodactyles : A, Left manus of Tapirus ; B, 

Bight manus of Titanotherium ; C, Left manus of Chalico- 
therium giganteum ........ 508 

107 Left manus of A, Coryphodon hamatus; B, Phenacodus pri- 

maevus ; C, Procavia (Dendrohyrax) arboreus . . . 510 

108 Left anterior and posterior limbs and Jimb girdles of Uinta- 

tHerium mirabile 516 

109 Left femur of an Ox (Bos taurus) and of a Sumatran Rhinoceros 

(Rhinoceros sumatrensis) 518 

110 Pes of A, a Tapir (Tapirus americanus) ; B, a Rhinoceros 

(Rhinoceros sumatremis) ; C, Hipparion gracile ; D, a Horse 
(Equus caballus) 524 



ERRATA. 

p. 172, note, for 14 read 15. 

p. 279, description of figure, for Tropidinotus read Tropidonotus. 
p. 287, description of figure, for shoulder-girdle of sternum read 

shoulder-girdle and sternum, 
p. 393, middle of page, for VIII read VII. 
p. 427, line 2, for Grampus read Killer. 



CHAPTER I. 

INTRODUCTORY ACCOUNT OF THE SKELETON IN 
GENERAL. 

BY the term skeleton is meant the hard structures whose 
function is to support or to protect the softer tissues of the 
animal body. 

The skeleton is divisible into 

A. The EXOSKELETOX, which is external ; 

B. The EXDOSKELETOX, which is as a rule internal : 
though in some cases, e.g. the antlers of deer, endoskeletal 
structures become, as development proceeds, external. 

In Invertebrates the hard, supporting structures of the 
body are mainly exoskeletal, in Vertebrates they are mainly 
endoskeletal ; but the endoskeleton includes, especially in 
the skull, a number of elements, the dermal or membrane 
bones, which are shown by development to have been originally 
of external origin. These membrane bones are so intimately 
related to the true endoskeleton that they will be described 
with it. The simplest and lowest types of both vertebrate 
and invertebrate animals have unsegmented skeletons ; with 
the need for flexibility however segmentation arose both in 
the case of the invertebrate exoskeleton and the vertebrate 
endoskeleton. The exoskeleton in vertebrates is phylogeneti- 
cally older than the endoskeleton, as is indicated by both 
R. 1 



2 THE VERTEBRATE SKELETON. 

palaeontology and embryology. Palaeontological evidence is 
afforded by the fact that all the lower groups of vertebrates 
Fish, Amphibia, and Reptiles had in former geological periods 
a greater proportion of species protected by well-developed 
dermal armour than is the case at present. Embryological 
evidence tends the same way, inasmuch as dermal ossifications 
appear much earlier in the developing animal than do the 
ossifications in the endoskeleton. 

Skeletal structures may be derived from each of the three 
germinal layers. Thus hairs and feathers are epiblastic in 
origin, bones are mesoblastic, and the notochord is hypo- 
blastic. 

The different types of skeletal structures may now be con- 
sidered and classified more fully. 

A. EXOSKELETAL STRUCTURES. 

I. EPIBLASTIC (epidermal). 

Exoskeletal structures of epiblastic origin may be developed 
on both the inner and outer surfaces of the Malpighian layer of 
the epidermis 1 . Those developed on the outer surface include 
hairs, feathers, scales, nails, beaks and tortoiseshell ; and 
are specially found in vertebrates higher than fishes. Those 
developed on the inner surface of the Malpighian layer include 
only the enamel of teeth and some kinds of scales. With 
the exception of feathers, which are partly formed from the 
horny layer, all these parts are mainly derived from the Mal- 
pighian layer of the epidermis. 

1 The skin consists of an outer layer of epiblastic origin, the 
epidermis, and an inner layer of mesoblastic origin, the dermis. The 
epidermis is divided into two principal layers, an outer one, the horny 
layer or stratum corneum, and an inner one, the stratum Malj>i<ihii. The 
innermost part of the .stratum corneum is distinguished as the stratum 
lucidum, and the outermost part of the stratum Malpighii as the stratum 
gramilosum. 



INTRODUCTORY. EPIBLASTIC STRUCTURES. 3 

Hairs are slender, elongated structures which arise by 
the proliferation of cells from the Malpighian layer of the 
epidermis. These cells in the case of each hair form a short 
papilla, which sinks inwards and becomes imbedded at the 
bottom of a follicle in the dermis. Each hair is normally 
composed of an inner cellular pithy portion containing much 
air, and an outer denser cortical portion of a horny nature. 
Sometimes, as in Deer, the hair is mainly formed of the pithy 
portion, and is then easily broken. Sometimes the horny part 
predominates, as in the bristles of Pigs. A highly vascular 
dermal papilla projects into the base of the hair. 

Feathers, like hairs, arise from epidermal papillae which 
become imbedded in pits in the dermis. But the feather germ 
differs from the hair germ, in the fact that it first grows 
out like a cone on the surface of the epidermis, and that 
the horny as well as the Malpighian layer takes part in its 
formation. 

Nails, claws, hoofs, and the horns of Oxen are also 
epidermal, as are such structures as the scales of reptiles, of 
birds 7 feet, and of Jfanis among mammals, the rattle of the 
rattlesnake, the nasal horns of Rhinoceros, and the baleen 
of whales. All these structures will be described later. 

Nails arise in the interior of the epidermis by the thicken- 
ing and cornification of the stratum lucidum. The outer 
border of the nail soon becomes free, and growth takes place 
by additions to the inner surface and attached end. 

When a nail tapers to a sharp point it is called a claw. 
In many cases the nails more or less surround the ends of 
the digits by which they are borne. 

Horny beaks of epidermal origin occur casing the jaw- 
bones in several widely distinct groups of animals. Thus 
among' reptiles they are found in Chelonia (tortoises and 
turtles) as well as in some extinct forms ; they occur in all 
living birds, in Ornithorhynchus among mammals, and in the 
larvae of many Amphibia. 

12 



4 THE VERTEBRATE SKELETON. 

In a few animals, such as Lampreys and Ornithorhynckus, 
the jaws bear horny tooth-like structures of epidermal origin. 

The enamel of teeth and of placoid scales is also epi- 
blastic in origin 1 , and it may be well at this point to give 
some account of the structure of teeth, though they are 
partly mesoblastic in origin. The simplest teeth are those 
met with in sharks and dogfish, where they are merely the 
slightly modified scales developed in the integument of the 
mouth. They pass by quite insensible gradations into normal 
placoid scales, such as cover the general surface of the body. 
A placoid scale 8 is developed on a papilla of the dermis 
which projects outwards and backwards, and is covered by the 
columnar Malpighian layer of the epidermis. The outer layer 
of the dermal papilla then gradually becomes converted into 
dentine and bone, while enamel is developed on the inner side 
of the Malpighian layer, forming a cap to the scale. The 
Malpighian and horny layers of the epidermis get rubbed off 
the enamel cap, so that it comes to project freely on the sur- 
face of the body. 

As regards their attachment teeth may be (1) attached 
to the fibrous integument of the mouth, or (2) fixed to the 
jaws or other bones of the mouth, or (3) planted in grooves, 
or (4) in definite sockets in the jaw-bones (see p. 107). 

Teeth in general consist of three tissues, enamel, dentine 
and cement, enclosing a central pulp-cavity containing blood- 
vessels and nerves. Enamel is, however, often absent, as in all 
living Edentates. 

Enamel generally forms the outermost layer of the crown 
or visible part of the tooth ; it is the hardest tissue occurring 
in the animal body and consists of prismatic fibres arranged ;it 
right angles to the surface of the tooth. It is characterised by 
its bluish-white translucent appearance. 

1 The enamel of the pharyngeal teeth of some Teleosteans is hypo- 
blastic in origin. 

2 See also p. 71. 



INTRODUCTORY. TEETH. 

II. MESOBLASTIC (mesodermal). 

Dentine or ivory generally forms the main mass of a 
tooth. It is a hard, white substance allied to bone. When 
examined microscopically dentine is seen to be traversed by 
great numbers of nearly parallel branching tubules which 
radiate outwards from the pulp-cavity. In fishes as a rule, 
and sometimes in other animals, a variety of dentine con- 
taining blood-vessels occurs, this is called vasodentine. 

Cement or cmsta petrosa forms the outermost layer of 
the root of the tooth. In composition and structure it is 
practically identical with bone. In the more complicated 
mammalian teeth, besides enveloping the root, it fills up the 
spaces between the folds of the enamel. 

The hard parts of a tooth commonly enclose a central pulp- 
cavity into which projects the pulp, a papilla of the dermis 
including blood-vessels and nerves. As long as growth con- 
tinues the outer layers of this pulp become successively calcified 
and added to the substance of the dentine. In young growing 
teeth the pulp-cavity remains widely open, but in mammals 
the general rule is that as a tooth gets older and the crown 
becomes fully formed, the remainder of the pulp becomes 
converted into one or more tapering roots which are im- 
bedded in the alveolar cavities of the jaws. The opening of 
the pulp-cavity is then reduced to a minute perforation at the 
base of each root. A tooth of this kind is called a rooted 
tooth. 

But it is not only in young teeth that the pulp-cavity 
sornetimes remains widely open ; for some teeth, such as the 
tusks of Elephants and the incisor teeth of Rodents, form 
no roots and continue to grow throughout the animal's 
life. Such teeth are said to be rootless or to have persistent 
pulps. 

An intermediate condition is seen in some teeth, such as 
the grinding teeth of Horses These teeth grow for a very 
long time, their crowns wearing away as fast as their bases 



THE VERTEBRATE SKELETON. 
// ^ in 







FIG. 1. DIAGRAMMATIC SECTIONS OF VARIOUS FORMS OF TEETH 
(from FLOWER). 

I. Incisor or tusk of elephant, with pulp-cavity persistently open at 
base. II. Human incisor during development with root imperfectly 
formed, and pulp-cavity widely open at base. III. Completely formed 
human incisor, with pulp-cavity contracted to a small aperture at the 
end of the root. IV. Human molar with broad crown and two roots. 
V. Molar of Ox, with the enamel covering the crown, deeply folded and 
the depressions filled with cement. The surface is worn by use, other- 
wise the enamel coating would be continuous at the top of the ridges. 
In all the figures the enamel is black, the pfyp white, the dentine 
represented by horizontal lines, and the cement by dots. 



INTRODUCTORY. TEETH. 7 

are produced; finally however definite roots are formed and 
growth ceases. 

The teeth of any animal may be homodont, that is, all 
having the same general character, or heterodont, that is, 
having different forms adapted to different functions. The 
dentition is heterodont in a few reptiles and the majority of 
mammals. 

SUCCESSION OF TEETH. In most fishes, and many amphibians 
and reptiles the teeth can be renewed indefinitely. In sharks, 
for example, numerous rows of reserve teeth are to be seen 
folded back behind those in use (see fig. 15). The majority of 
mammals have only two sets of teeth, and are said to be diphy- 
odont ; some have only a single series (monophyodont). 

DEVELOPMENT OF TEETH. A brief sketch of the method in 
which development of teeth takes place in the higher verte- 
brates may here be given. Along the surface of the jaws a 
thickening of .-the epiblastic epithelium takes place, giving rise 
to a ridge, which sinks inwards into the tissue of the jaw, 
and it is known as the primary enamel organ. At the points 
where teeth are to be developed special ingrowths of this 
; primary enamel organ take place, and into each there projects 
a vascular dental papilla from the surrounding mesoblast of 
the jaw. Each ingrowth of the enamel organ forms an 
enamel cap, which gradually embraces the dental papilla, 
and at the same time appears to be pushed on one side, owing 
to the growth not being uniform. The external layer of 
the dental papilla is composed of long nucleated cells, the 
odontoblasts, and it is by these that the dentine is formed. 
Similarly the internal layer of the enamel organ is formed of 
columnar enamel cells, which give rise to the enamel. The 
mesoblastic cells surrounding the base of the tooth give rise 
to the cement. 

Bone is in many cases exoskeletal, but it will be most 
conveniently described with the endoskeleton. 



8 THE VERTEBRATE SKELETON. 

The scales of fish are wholly or in part mesoblastic 
in origin, being totally different from those of reptiles. The 
cycloid and ctenoid scales of Teleosteans (see p. 105) are thin 
plates coated with epidermis. They are sometimes bony, but 
as a rule are simply calcined. Ganoid scales are flat plates 
of bone coated with an enamel-like substance, and articulating 
together with a peg and socket arrangement; they are pro- 
bably identical with enlarged and flattened placoid scales. 

The armour plates of fossil Ganoids, Labyrinthodonts, 
and Dinosaurs, and of living Crocodiles, some Lizards and 
Armadillos, are composed of bone. They are always covered 
by a layer of epidermis. 

The antlers of deer are also composed of bone; they 
will be more fully described in the chapter on mammals. 
It may perhaps be well to mention them here, though they 
really belong to the endoskeleton, being outgrowths from the 
frontal bones. 

B. ENDOSKELETAL STRUCTURES. 
I. HYPOBLASTIC. 

(a) The notochord is an elastic rod formed of large 
vacuolated cells, and is surrounded by a membranous sheath ' 
of mesoblastic origin. It is the primitive endoskeleton in 
the Chordata, all of which possess it at some period of their 
existence; while in many of the lower forms it persists through- 
out life. Even in the highest Chordata it is the sole repre- 
sentative of the axial skeleton for a considerable part of the 
early embryonic life. A simple unsegmented notochord 
persists throughout life in the Cephalochordata, Cyclostomata, 
and some Pisces, such as Sturgeons and Chimaeroids. 

(b) The enamel of the pharyngeal teeth of the Salmon 
and many other Teleosteans is hypoblastic in origin. The 
epiblast of the stomodaeum, in which the other teeth are 
developed, passes into the hypoblast of the mesenteron in 
which these pharyngeal teeth are formed. 



INTRODUCTORY. BONE. 9 

II. MESOBLASTIC. 

The most primitive type of a mesoblastic endoskeleton 
consists of a membranous sheath surrounding the notochord, 
as in ^fyxine and its allies. The first stage of complication 
is by the development of cartilage in the notochordal sheath, 
as in Petromyzon. Often the cartilage becomes calcified in 
places, as in the vertebral centra of ScyUium and other Elas- 
mobranchs. Lastly, the formation of bone takes place ; it 
generally constitutes the most important of the endoskeletal 
structures. 

Bone may be formed in two ways : 

(1) by the direct ossification of pre-existing cartilage, 
when it is known as cartilage bone or endochondral bone : 

(2) by independent ossification in connective tissue ; it is 
then known as membrane or dermal or periosteal bone. 

With the exception of the clavicle 1 all the bones of the trunk 
and limbs, together with a large proportion of those of the 
skull, are preformed in the embryo in cartilage, and are grouped 
as cartilage bones : while the clavicle and most of the roofing 
and jaw-bones of the skull are not preformed in cartilage, being 
developed simply in connection with a membrane. Hence it 
is customary to draw a very strong line of distinction between 
these two kinds of bone; in reality however this distinction 
is often exaggerated, and the two kinds pass into one another, 
and as will be shown immediately, the permanent osseous 
tissue of many of those which are generally regarded as 
typical cartilage bones, is really to a great extent of periosteal 
origin. The palatine bone, for instance, of the higher verte- 
brates in general is preceded by a cartilaginous bar, but is 
itself almost entirely a membrane bone. 

Before describing the development of bone it will be well 
to briefly describe the structure of adult bone and cartilage. 

1 It is usual to regard the clavicle as a membrane bone, but Kiilliker 
has shown that in rabbit embryos of about the 17th day it is cartilaginous. 



10 THE VERTEBRATE SKELETON. 

The commonest kind of cartilage, and that which pre- 
forms so many of the bones of the embryo, is hyaline cartilage. 
It consists of oval nucleated cells occupying cavities (lacunae) 
in a clear intercellular semitransparent matrix, which is pro- 
bably secreted by the cells. Sometimes one cell is seen in each 
lacuna, sometimes shortly after cell-division a lacuna may con- 
tain two or more cells. The free surface of the cartilage 
is invested by a fibrous membrane, the perichondrium. 

Bone consists of a series of lamellae of ossified substance 
between which are oval spaces, the lacunae, giving rise to 
numerous fine channels, the canaliculi, which radiate off in 
all directions. The lacunae are occupied by the bone cells 
which correspond to cartilage cells, from which if the bone is 
young, processes pass off into the canaliculi. It is obvious 
that the ossified substance of bone is intercellular in character, 
and corresponds to the matrix of cartilage. 

Bone may be compact, or loose and spongy in character, 
when it is known as cancellous bone. In compact bone 
many of the lamellae are arranged concentrically round 
cavities, the Haversian canals, which in life are occupied by 
blood-vessels. Each Haversian canal with its lamellae forms 
a Haversian system. In spongy bone instead of Haversian 
canals there occur large irregular spaces filled with marrow, 
which consists chiefly of blood-vessels and fatty tissue. The 
centre of a long bone is generally occupied by one large con- 
tinuous marrow cavity. The whole bone is surrounded by 
a fibrous connective tissue membrane, the periosteum. 

THE DEVELOPMENT OF BONE. 

Periosteal ossification. An example of a bone en- 
tirely formed in this way is afforded by the parietal. The 
first trace of ossification is shown by the appearance, below 
the membrane which occupies the place of the bone in the 
early embryo, of calcareous spicules of bony matter, which 
are laid down round themselves by certain large cells, the 



INTRODUCTORY. DEVELOPMENT OF BONE. 11 

osteoblasts. These osteoblasts gradually get surrounded by 
the matter which they secrete and become converted into bone 
cells, and in this way a mass of spongy bone is gradually pro- 
duced. Meanwhile a definite periosteum has been formed round 
the developing bone, and on its inner side fresh osteoblasts 
are produced, and these with the others gradually render the 
bone larger and more and more compact. Finally, the middle 
layer of the bone becomes again hollowed out and rendered 
spongy by the absorption of part of the bony matter. 

Endochondral ossification 1 . This is best studied in the 
case of a long bone like the femur or humerus. Such a long 
bone consists of a shaft, which forms the main part, and two 
terminal portions, which form the epiphyses, or portions 
ossifying from centres distinct from that forming the shaft or 
main part of the bone. 

In the earliest stage the future bone consists of hyaline 
cartilage surrounded by a vascular sheath, the perichondrium. 

Then, starting from the centre, the cartilage becomes per- 
meated by a number of channels into which pass vessels from 
the perichondrium and osteoblasts. In this way the centre 
of the developing shaft becomes converted into a mass of 
cavities separated by bands or trabeculae of cartilage. This 
cartilage next becomes calcined, but as yet is not converted 
into true bone. The osteoblasts in connection with the 
cavities now begin to deposit true endochondral spongy bone, 
and then after a time this becomes absorbed by certain 
large cells, the osteoclasts, and resolved into marrow or vas- 
cular tissue loaded with fat. So that the centre of the shaft 
passes from the condition of hyaline cartilage to that of 
calcined cartilage, thence to the condition of spongy bone, and 
finally to that of marrow. At the same time beneath the 

1 In compiling these paragraphs on Histology, free use has been 
made of Klein and Noble Smith's Atlas of Histology, the small Histo- 
logies of Klein and Schafer, Huxley's Elementary Physiology, and Lloyd 
Morgan's Animal Bioloyy. 



12 THE VERTEBRATE SKELETON. 

perichondrium osteoblasts are developed which also begin to 
give rise to spongy bone. The perichondrium thus becomes 
the periosteum, and the bone produced by it, is periosteal or 
membrane bone. So that while a continuous marrow cavit}* is 
gradually being formed in the centre of the shaft, the layer of 
periosteal bone round the margin is gradually thickening, and 
becoming more and more compact by the narrowing down of its 
cavities to the size of Haversian canals. The absorption of 
endochondral and formation of periosteal bone goes on, till 
in time it comes about that the whole of the shaft, except 
its terminations, is of periosteal origin. At the extremities 
of the shaft, however, and at the epiphyses, each of which 
is for a long time separated from the shaft by a pad of 
cartilage, the ossification is mainly endochondral, the peri- 
osteal bone being represented only by a thin layer. 

Until the adult condition is reached and growth ceases, the 
pad of cartilage between the epiphysis and the shaft continues 
to grow, its outer (epiphysial) half growing by the formation of 
fresh cartilage as fast as its inner half is encroached on by the 
growth of bone from the shaft. The terminal or articular 
surfaces of the bone remain throughout life covered by layers 
of articular cartilage. 

Even after the adult condition is reached the bone is 
subject to continual change, processes of absorption and fresh 
formation going on for a time and tending to render the bone 
more compact. 

METHODS IN WHICH BONES ARE UNITED TO ONE ANOTHER. 

The various bones composing the endoskeleton are united 
to one another either by sutures or by movable joints. 

When two bones are suturally united, their edges fit 
closely together and often interlock, being also bound together 
by the periosteum. 

In many cases this sutural union passes into fusion or 
ankylosis, ossification extending completely from one bone to 



INTRODUCTORY. JOINTS. 13 

the other with the obliteration of the intervening suture. This 
feature is especially well marked in the cranium of most birds. 

The various kinds of joints or articulations' may be sub- 
divided into imperfect joints and perfect joints. 

In imperfect joints, such as the intervertebral joints of 
mammals, the two contiguous surfaces are united by a mass 
of fibrous tissue which allows only a limited amount of motion. 

In perfect joints the contiguous articular surfaces are 
covered with cartilage, and between them lies a synovial 
membrane which secretes a viscid lubricating fluid. 

The amount of motion possible varies according to the 
nature of the articular surfaces : these include 

a. ball and socket joints, like the hip and shoulder, in 
which the end of one bone works in a cup provided by an- 
other, and movements can take place in a variety of planes. 

b. hinge joints, like the elbow and knee, in which as 
in ball-and-socket joints one bone works in a cup provided 
by another, but movements can take place in one plane only. 

THE EXDOSKELETON. 

The endoskeleton is divisible into axial and appendi- 
cular parts ; and the axial skeleton into 

1. the spinal column, 

ta. the cranium, 

2. the skull ' 



r 

\b. 



the jaws and visceral skeleton, 
3. the ribs and sternum 2 . 

I. THE AXIAL SKELETON*. 

1. THE SPINAL COLUMN. 

The spinal column in the simplest cases consists of an 

1 See Huxley's Elementary Physiology, Revised edition, London, 1886, 
p. 180. 

ictly speaking the jaws, visceral skeleton, ribs and sternum do 
not form part of the axis, but it is convenient to group them as parts of 
the axial skeleton. 



14 THE VERTEBRATE SKELETON. 

unsegmented rod, the notochord, surrounded by the skeleto- 
genous layer, a sheath of mesoblastic origin, which also 
envelops the nerve cord. Several intermediate stages connect 
this simple spinal column with the vertebral column charac- 
teristic of higher vertebrates. A typical vertebral column 
may be said to consist of (1) a series of cartilaginous or bony 
blocks, the vertebral centra, which arise in the sheath 
surrounding the notochord. They cause the notochord to 
become constricted and to atrophy to a varying extent, though 
a remnant of it persists, either permanently or for a long 
period, within each centrum or between successive centra. 
(2) From the dorsal surface of each centrum arise a pair of 
processes which grow round the spinal cord and unite above 
it, forming a dorsal or neural arch. (3) A similar pair 
of processes arising from the ventral surface of the centrum 
form the ventral or haemal arch. To the ventral arch 
the ribs strictly belong, and it tends to surround the ventral 
blood-vessels and the body cavity with the alimentary canal 
and other viscera. 

A neural spine or spinous process commonly projects 
upwards from the dorsal surface of the neural arch, and a pair 
of transverse processes project outwards from its sides. 
When, as is commonly the case, the two halves of the haemal 
arch do not meet, the ventral surface of the centrum often 
bears a downwardly-projecting hypapophysis. 

The character of the surfaces by which vertebral centra 
articulate with one another varies much. Sometimes both 
surfaces are concave, and the vertebra is then said to be 
amphicoelous ; sometimes a centrum is convex in front and 
concave behind, the vertebra is then opisthocoelous, some- 
times concave in front and convex behind, when the vertebra 
is procoelous. Again, in many vertebrae both faces of the 
centra are flat, while in others they are saddle- shaped, as in the 
neck vertebrae of living birds, or biconvex, as in the case of 
the first caudal vertebra of crocodiles. 



INTRODUCTORY. VERTEBRAE. 



In the higher vertebrates pads of fibro-cartilage the 
intervertebral discs are commonly interposed between 




10 



FIG. 2. CERVICAL VERTEBRAE OF AX Ox (Bos taurus). 



A, is the fifth; B, the fourth; C, the third. 
1. neural spine. 



(Camb. Mus. ) 



2. transverse process. 

3. hypapophysis. 

4. convex anterior face of the 

centrum. 

5. concave posterior face of the 

centrum. 



6. prezygapophysis. 

7. postzygapophysis. 

8. vertebrarterial canal. 

9. neural canal. 

10. inferior lamella of transverse 
process. 



successive centra, these or parts of them often ossify, especially 
in the trunk and tail, and are then known as intercentra. 

The vertebrae of the higher forms can generally be arranged 
in the following five groups, each marked by certain special 
characteristics : 

1. The cervical or neck vertebrae. These connect 
the skull with the thorax, and are characterised by relatively 
great freedom of movement. They often bear small ribs, but 
are distinguished from the succeeding thoracic vertebrae by 
the fact that their ribs do not reach the sternum. The first 
cervical vertebra which articulates with the skull is called 
the atlas, but a study of the nerve exits shows that the first 



16 THE VERTEBRATE SKELETON. 

vertebra is not serially homologous throughout the Ichthy- 
opsida, so that it is best to reserve the term atlas for the first 
vertebra in Sauropsida and Mammalia. 

2. The thoracic vertebrae (often called dorsal) bear 
movably articulated ribs which unite ventrally with the 
sternum. 

3. The lumbar vertebrae are generally large, and are 
often more movable on one another than are the thoracic 
vertebrae. They bear no ribs. 

4. The sacral vertebrae are characterised by the fact 
that they are firmly fused together, and are united with the 
pelvic girdle by means of their transverse processes and rudi- 
mentary ribs. 

5. The caudal or tail vertebrae succeed the sacral. 
The anterior ones are often fused with one another and with 
the sacrals, but they differ from true sacral vertebrae in that 
there are no rudimentary ribs between their transverse pro- 
cesses and the pelvic girdle. They often bear V-shaped 
chevron bones. 

In fish and snakes the vertebral column is divisible into 
only two regions, an anterior trunk region, whose vertebrae bear 
ribs, and a posterior tail region, whose vertebrae are ribless. 

2. THE SKULL. 

Before giving a general account of the adult skull it will 
be well to briefly describe its development. 

GENERAL DEVELOPMENT OF THE CRANIUM l . 

Shortly after its appearance, the central nervous system 
becomes surrounded by a membranous mesodermal investment 
which in the region of the spinal cord is called the skeleto- 
genous layer or perichordal sheath, while in the region 

1 F. M. Balfour, Comparative Embryology, vol. n., London, 1881, 
p. 465. W. K. Parker and G. T. Bettany, The Morphology of the Skull, 
London, 1877. 



INTRODUCTORY. DEVELOPMENT OF THE CRANIUM. 17 

of the brain it is called the membranous cranium. Ventral 
to the central nervous system is the notochord, which extends 
far into the region of the future cranium, and like the 
nervous system, is enclosed by the skeletogenous layer. The 
primitive cartilaginous cranium is formed by histological 
differentiation within the substance of the membranous 
cranium and always consists of the following parts : 

(a) the parachordals. These are a pair of flat curved 
plates of cartilage, each of which has its inner edge grooved 
where it conies in contact with the notochord. The para- 
chordals, together with the notochord, form a continuous 
plate, which is known as the basilar plate. The basilar 
plate is the primitive floor below the hind- and mid-brain. 
In front the parachordals abut upon another pair of carti- 
laginous bars, the traljeculae, the two pairs of structures being 
sometimes continuous with one another from the first : 

(6) the trabeculae which meet behind and embrace the 
front end of the notochord. Further forwards they at first 
diverge from one another, and then converge again, enclosing 
a space, the pituitary space. After a time they generally 
fuse with one another in the middle line, and, with the para- 
chordals behind, form an almost continuous basal plate. The 
trabeculae generally appear before the parachordals. They 
form the primitive floor below the fore-brain ; 

(c) the cartilaginous capsules of the three pairs of sense 
organs. At a very early stage of development involutions 
of the surface epiblast give rise to the three pairs of special 
sense organs the olfactory or nasal organs in front, the optic 
in the middle, and the auditory behind. The olfactory and 
auditory organs always become enclosed in definite cartilagi- 
nous capsules, the eyes often as in the Salmon, become 
enclosed in cartilaginous sclerotic capsules, while sometimes, 
as in mammals, their protecting capsules are fibrous. 

Each pair of sense capsules comes into relation with part 
R. 2 



18 THE VERTEBRATE SKELETON. 

of the primitive cranium, and greatly modifies it. Thus the 
auditory or periotic capsules press on the parachordals till 
they come to be more or less imbedded in them. Perhaps 
owing to the pressure of the nasal capsules the trabeculae 
fuse in front, and then grow out into an anterior pair of 
processes, the cornua trabeculae, and a posterior pair, the 
antorbital processes, which together almost completely sur- 
round the nasal capsules. The sclerotic capsules of the eyes 
greatly modify the cranium, although they never become 
completely united with it. 

The cartilaginous cranium formed of the basal plate, to- 
gether with the sense capsules, does not long remain merely 
as a floor. Its sides grow vertically upwards, forming the 
exoccipital region of the cranium behind, and the ali- 
sphenoidal and orbitosphenoidal regions further forwards. 
In many forms, such as Elasmobranchs, all these upgrowths 
meet round the brain, roofing it in and forming an almost 
complete cartilaginous cranium. But in most vertebrata, 
while in the occipital region, the cartilaginous cranium is 
completed dorsally, in the alisphenoidal and orbitosphenoidal 
regions the cartilage merely forms the lateral walls of the 
cranium, the greater part of the brain having dorsal to it a 
wide space, closed by merely membranous tissue in connection 
with which the large frontal and parietal bones are subse- 
quently formed. 

The SKULL includes 

a. the cranium, 

b. the jaws and visceral skeleton. 

The cranium can be further subdivided into 

(1) an axial portion, the cranium proper or brain 
case; 

(2) the sense capsules. The capsules of the auditory 
and olfactory sense organs are always present, and as has been 



IXTRCMMTCTORY. THE CRANIUM. 19 

already mentioned, in many animals the eye likewise is 
included in a cartilaginous capsule. 

(1) THE CRANIUM PROPER Or BRAIX CASE. 

The cranium varies much in form and structure. In lower 
vertebrates, such as Sharks and Lampreys, it remains entirely 
cartilaginous and membranous, retaining throughout life much 
of the character of the embryonic rudiment of the cranium of 
higher forms. The dogfish's cranium, described on pp. 73 to 
76, is a good instance of a cranium of this type. But in the 
majority of vertebrates the cartilage becomes more or less 
replaced by cartilage bone, while membrane bones are also 
largely developed and supplant the cartilage. 

The cranium of most vertebrates includes a very large 
number of bones whose arrangement varies much, but one 
can distinguish a definite basicranial axis formed of the 
basi-occipital, basisphenoid, and presphenoid bones, which is 
a continuation forwards of the axis of the vertebral column. 
From the basicranial axis a wide arch arises, composed of a 
number of bones, which form the sides and roof of the brain- 
case. These bones are arranged in such a manner that if both 
cartilage and membrane bones are included they can be divided 
into three rings or segments. The hinder one of these seg- 
ments is the occipital, the middle the parietal, and the anterior 
one the frontal. 

The occipital segment is formed of four cartilage bones, the 
basi-occipital below, two exoccipitals at the sides, and the 
supra-occipital above. The parietal segment is formed of 
the basisphenoid below, two alisphenoids at the sides and 
two membrane bones, the parietals above, and the frontal 
segment in like manner consists of the presphenoid below, 
the two orbitosphenoids at the sides, and two membrane 
bones, the frontals, above. The parietals and frontals, being 
membrane bones, are not comparable to the supra-occipital, 
in the way that the presphenoid and basisphenoid are to the 
basi-occipital. 

22 



20 THE VERTEBRATE SKELETON. 

The cartilage bones of the occipital segments are derived 
from the parachordals of the embryonic skull, those of the 
parietal and frontal segments from the trabeculae. 

In front of the presphenoid the basicranial axis is con- 
tinued by the mesethmoid. 

(2) THE SENSE CAPSULES. 

These enclose and protect the special sense organs. 

() Auditory capsule. 

The basisphenoid is always continuous with the basi- 
occipital, but the alisphenoid is not continuous with the ex- 
occipital as the periotic or auditory capsule is interposed 
between them. Each periotic capsule has three principal 
ossifications ; an anterior bone, the pro -otic, a posterior bone, 
the opisthotic, and a superior bone, the epi-otic. 

These bones may severally unite, or instead of uniting 
with one another they may unite with the neighbouring bones. 
Thus the epi-otic often unites with the supra-occipital, and the 
opisthotic with the exoccipital. 

Two other bones developed in the walls of the auditory 
capsule are sometimes added, as in Teleosteans ; these are the 
pterotic and sphenotic. 

(6) Optic capsule. 

The eye is frequently enclosed in a cartilaginous sclerotic 
capsule, and in this a number of scale-like bones are often 
developed. 

Several membrane bones are commonly formed around the 
orbit or cavity for the eye. The most constant of these is 
the lachrymal which lies in the anterior corner; frequently too, 
as in Teleosteans, there is a supra-orbital lying in the upper 
part of the orbit, or as in many Reptiles, a postorbital lying in 
the posterior part of the orbit. 

(c) Nasal capsule. 

In relation to the nasal capsules various bones occur. 



INTRODUCTORY. JAWS AND VISCERAL SKELETON. 21 

The basicranial axis in front of the presphenoid is ossified, 
as the mesethmoid, dorsal to which there sometimes, as in 
Teleosteans, occur a median ethmoid and a pair of lateral 
ethmoids 1 . Two pairs of membrane bones very commonly 
occur in this region, viz. the tiasals which lie dorsal to the 
mesethmoid, and the vomers (sometimes there is only one) which 
lie ventral to it. 

The part of the skull lying immediately in front of the 
cranial cavity and in relation to the nasal capsules constitutes 
the ethmoidal region. 

There remain certain other membrane bones which are 
often found connected with the cranium. Of these, one of 
the largest is the parasphenoid which, in Ichthyopsids, is 
found underlying the basicranial axis. Prefrantals often, as 
in most reptiles, occur lying partly at the sides and partly in 
front of the frontal, and postfrontala similarly occur behind the 
orbit lying partly behind the frontals and partly at their sides. 
Lastly a squamosal bone is, as in Mammals, very commonly 
developed, and lies external and partly dorsal to the auditory 
capsules. 

THE JAWS AND VISCERAL SKELETON. 

In the most primitive fish these consist of a series of 
cartilaginous rings or arches placed one behind another and 
encircling the anterior end of the alimentary canal. Originally 
they are mainly concerned with branchial respiration. 

The first or maxillo-mandibular arch forms the upper 
jaw and the lower jaw or mandible. 

The second or hyoid arch bears gills and often assists 
in attaching the jaws to the cranium. The remaining arches 
may bear gills, though the last is commonly without them. 

The above condition is only found in fishes, in higher 
animals the visceral skeleton is greatly reduced and modified. 

The first or maxillo-mandibular arch is divisible into a 

1 Sometimes also called ectethmoids or parethmoids. 



22 THE VERTEBRATE SKELETON. 

dorsal portion, the palato-pterygo-quadrate bar, which 
forms the primitive upper jaw and enters into very close 
relations with the cranium, and a ventral portion, Meckel's 
cartilage, which forms the primitive lower jaw. The carti- 
laginous rudiments of both these portions disappear to a 
greater or less extent and become partly ossified, partly re- 
placed by or enveloped in membrane bone. 

The posterior part of the palato-pterygo-quadrate bar be- 
comes ossified to form the quadrate, the anterior part to form 
the palatine and pterygoid, or the two latter may be formed 
partially or entirely of periosteal bone, developed round the 
cartilaginous bar. Two pairs of important membrane bones, 
the premaxillae and maxillae form the anterior part of the 
upper jaw, and behind the maxilla lies another membrane 
bone, the jugal or malar, which is connected with the quadrate 
by a quadratojugal. The premaxillae have a large share in 
bounding the external nasal openings or anterior nares. 

In lower vertebrates the nasal passage leads directly into 
the front part of the mouth cavity and opens by the posterior 
nares. In some higher vertebrates, such as mammals and 
crocodiles, processes arise from the premaxillae and palatines, 
and sometimes from the pterygoids, which meet their fellows 
in the middle line and form the palate, shutting off the nasal 
passage from the mouth cavity and causing the posterior nares 
to open far back. 

The cartilage of the lower jaw is in all animals with 
ossified skeletons, except the Mammalia, partly replaced by 
cartilage bone forming the articular, partly overlain by a 
series of membrane bones the dentary, splenial, angular, 
supra-angular and coronoid. In many sharks large paired 
accessory cartilages occur at the sides of the jaws ; and in a 
few reptiles and some Amphibia, such as the Frog, the ossified 
representative of the anterior of these structures occurs 
forming the mento-meckelian bone. In mammals the lower 
jaw includes but a single bone. 



INTRODUCTORY. RIBS AND STERNUM. 23 

The quadrate in all animals with ossified skeletons, except 
the Mammalia, forms the suspensorium of the mandible or the 
skeletal link between the jaw and the cranium ; in the Mam- 
malia, however, the mandible articulates with the squamosal, 
while the quadrate is greatly reduced, and is now generally 
considered to be represented by the tympanic ring of the ear. 

The second visceral or hyoid arch in fishes consists of two 
pieces of cartilage, a proximal 1 piece the hyomandibular, 
and a distal 1 piece the cerato-hyal. The cerato-hyals of the 
two sides are commonly united by a median ventral plate, the 
basi-hyal. The hyoid arch bears gills on its posterior border, 
but its most important function in most fishes is to act as the 
suspensorium. In higher vertebrates the representative of 
the hyomandibular is much reduced in size, and covnes into 
relation with the ear forming the auditory ossicles; the 
cerato-hyal looses its attachment to the hyomandibular and 
becomes directly attached to the cranium, forming a large part 
of the hyoid apparatus of most higher vertebrates. 

Behind the hyoid arch come the branchial arches. They 
are best developed in fishes, in which they are commonly five 
in number and bear gills. Their ventral ends are united in 
pairs by median pieces, the copulae. 

In higher vertebrates they become greatly reduced, and 
all except the first and second completely disappear. In the 
highest vertebrates, the mammals, the second has disappeared, 
but. in birds and many reptiles it is comparatively well 
developed. 

3. THE RIBS AND STERNUM. 

The ribs are a series of segmentally arranged cartilagi- 
nous or bony rods, attached to the vertebrae ; they tend 
to surround the body cavity, and to protect the organs 
contained within it. Ribs are very frequently found 

1 The proximal end of anything is the one nearest the point of origin 
or attachment, the distal end is the one furthest from the point of origin 
or attachment. 



24 THE VERTEBRATE SKELETON. 

attached to the transverse processes of the vertebrae, but a 
study of their origin in fish shows that they are really the 
cut off terminations of the ventral arch, not of the transverse 
processes which are outgrowths from the dorsal arch. In the 
tail their function is to surround and protect structures like 
the ventral blood-vessels which do not vary much in size, 
consequently they meet one another, and form a series of 
complete ventral or haemal arches. But the trunk contains 
organs like the lungs and stomach which are liable to vary 
much in size at different times, consequently the halves of the 
haemal arch do not meet ventrally, and then the ribs become 
detached from the rest of the haemal arch. Having once 
become detached, they are able to shift about and unite them- 
selves to various points of the vertebra. They frequently, as 
has been already mentioned, become entirely attached to the 
transverse process, or they may be attached to the transverse 
process by a dorsal or tubercular portion and to the centrum 
or to the ventral arch by a ventral or capitular portion. 

In all animals above fishes the distal ends of the thoracic 
ribs unite with a median breast bone or sternum which 
generally has the form of a segmented rod. The sternum is 
really formed by the fusion of the distal ends of a series of 
ribs. In many animals elements of the shoulder girdle enter 
into close relation with the rib elements of the sternum. 

II. THE APPENDICULAK SKELETON. 

This consists of the skeleton of the anterior or pectoral, 
and the posterior or pelvic limbs, and their girdles. In every 
case (except in Chelonia) the parts of the appendicular skele- 
ton lie external to the ribs. 

1. THE LIMB GIRDLES. 

The Pectoral girdle 1 . In the simplest case the pectoral 
or shoulder girdle consists of a hoop of cartilage incomplete 

1 W. K. Parker, A Monograph of the Shoulder Girdle and Sternum, 
Ray Soc. London, 1868. 



INTRODUCTORY. LIMB GIRDLES. 25 

dorsally. It is attached by muscle to the vertebral column, 
and is divided on either side into dorsal and ventral portions 
by a cavity, the glenoid cavity, at the point where the 
anterior limb articulates. In higher fishes this hoop is dis- 
tinctly divided into right and left halves ; it becomes more or 
less ossified, and a pair of important bones, the clavicles, are 
developed in connection with its ventral portion. 

In higher vertebrates ossification sets up in the cartilage 
and gives rise on each side to a dorsal bone, the scapula, 
and frequently to an anterior ventral bone, the precoracoid, 
and a posterior ventral bone, the coracoid. The precoracoid 
is often not ossified, and upon it is developed the clavicle 
which more or less replaces it. In some forms a T shaped 
interdavicle occurs, in others epicoracoids are found in front 
of the coracoids. In all vertebrata above fish, except the great 
majority of mammals, the coracoids are large and articulate 
with the sternum. But in mammals the coracoids are nearly 
always quite vestigial, and the pectoral girdle is attached to 
the axial skeleton by the clavicle or sometimes by muscles and 
ligaments only. 

The Pelvic girdle 1 like the pectoral consists primitively 
of a simple rod or hoop of cartilage, which in vertebrata above 
fishes is divided into dorsal and ventral portions, by a cavity, 
the acetabulum, with which the posterior limb articulates. 
In the pelvic girdle as in the pectoral one dorsal, and (com- 
monly) two ventral ossifications take place. The dorsal bone 
is the ilium and corresponds to the scapula. The posterior 
ventral bone is the ischium corresponding to the coracoid. 
The anterior ventral bone is the pubis and is generally com- 
pared to the precoracoid, but in some cases a fourth pelvic 
element, the acetabular or cotyloid bone is found, and this 
may correspond to the precoracoid. 

The pelvic girdle differs from the pectoral in the fact that 
the dorsal bones the ilia are nearly always firmly united to 
1 See R. Wiedersheim, Zeitschr. iciss. Zool. vol. Lin. suppl. p. 43, 1892. 



26 THE VERTEBRATE SKELETON. 

transverse processes of the sacral vertebrae, by means of 
rudimentary ribs. The pubes and ischia generally meet in 
ventral symphyses. 

2. THE LIMBS. 

It will be most convenient to defer a discussion of the 
limbs of fishes to chap. vui. 

All vertebrates above fishes have the limbs divisible into 
three main segments : 

Anterior or Fore limb. Posterior or Hind limb. 
Proximal segment. upper arm or brachium. thigh. 

Middle segment. fore-arm or antibrachium. shin or cms. 

Distal segment. manus. pes. 

The proximal segments each contain one bone, the hume- 
rus in the case of the upper arm, and the femur in the case 
of the thigh. The middle segments each contain two bones, 
the radius and ulna in the case of the fore-arm, and the tibia 
and fibula in the case of the shin. 

The manus and pes are further subdivided into 

(a) two or three proximal rows of bones forming the 
wrist or carpus in the case of the manus, and the ankle or 
tarsus in the case of the pes. 

(6) a middle row called respectively the metacarpus 
and metatarsus. 

(c) a number of distal bones called the phalanges 
which form the skeleton of the fingers and toes, or digits. 

Typically the manus and pes both have five digits (pente- 
dactylate). The first digit of the manus is commonly called 
the pollex, and the first digit of the pes the hallux. 

In a very simple carpus such as that of Chelydra, there 
are nine bones. They are arranged in a proximal row of 



INTRODUCTORY. THE LIMES. 27 

three, the radiale, intermedium, and ulnare, the first being 
on the radial side of the limb, and a distal row of five called 
respectively carpale 1, 2, 3, 4, 5, beginning on the radial side. 
Between these two rows is a single bone the centrale, or there 
may be two. 

Similarly there are nine bones in a simple tarsus such as 
that of Scdamandra. They form a proximal row of three, the 
tibiale, intermedium and fibulare, and a distal row of five, 
called respectively tarsale 1, 2, 3, 4, 5, beginning on the tibial 
side. Between the two rows there is a centrale as in the 
carpus, or there may be two. 

The following names derived from human anatomy are 
commonly applied to the various carpal and tarsal bones : 

Carpus. Tarsus. 

radiale = scaphoid tibiale ) 

,. * t astragalus 

i ntermedium = lunar intermedium j 

ulnare = cuneiform fibulare calcaneum 

centrale = central centrale = navicular 

carpale 1 = trapezium tarsale 1 = internal cuneiform 
,, 2 = trapezoid ,, 2 = middle 

,, 3 = magnum 3 = external 



,1 =nnciform " I = 

J 5J 



cuboid 



NOTE. The above is the view commonly accepted concerning the 
homology of the carpal and tarsal bones. But with regard to the 
proximal row of tarsal bones there is difference of opinion. All anato- 
mists are agreed that the calcaneum is the fibulare and that the inter- 
medium is contained in the astragalus, but while the majority regard 
the astragalus as the fused tibiale and intermedium, Baur considers 
that a small bone found on the tibial side of the tarsus in Procavia, 
many Rodents, Insectivores, and the male Ornithorhynchus, is the vesti- 
gial tibiale, and regards the astragalus as the intermedium alone 1 . He 
also considers that the mammalian scaphoid represents a centrale. 

1 G. Baur, Beitrcige zur Horphogenie des Carpus und Tarsus der 
I'ertebraten, Theil 1. Batrachia. Jena, 1888, and Amer. Natural., vol. xix. 
1885 (several papers). 



28 THE VERTEBRATE SKELETON. 

MODIFICATIONS IN THE POSITIONS OP THE LIMBS'. 

In their primitive position the limbs are straight and are 
extended parallel to one another at right angles to the axis of 
the trunk. Each limb then has a dorsal surface, a ventral 
surface, an anterior or pre-axial edge, and a posterior or 
postaxial edge. 

In the anterior limb the radius and the pollex are pre- 
axial, the ulna and the fifth finger are postaxial. In the 
posterior limb the tibia and the hallux are pre-axial, the fibula 
and the fifth toe are postaxial. The Cetacea and various extinct 
reptiles, such as Ichthyosaurus and Plesiosaurus, have their 
limbs in practically this primitive position. 

The first modification from it is produced by the bending 
ventrally of the middle segments of both limbs upon the 
proximal segments, while the distal segment is bent in the 
opposite direction on the middle segment. Then the ventral 
surfaces of the antibrachium and crus come to look inwards, 
and their dorsal surfaces to look outwards. The brachium 
and manus, thigh and pes still have their dorsal surfaces 
facing upwards and their ventral surfaces facing downwards 
as before, and the relations of their pre- and postaxial borders 
remain as they were. Many Amphibians and Reptiles, such 
as tortoises, carry their limbs in this position. 

In all higher vertebrates, however, a further change takes 
place, each limb is rotated as a whole from its proximal end, 
the rotation taking place in opposite directions in the fore and 
hind limbs respectively. The anterior limb is rotated back- 
wards from the shoulder, so that the brachium lies nearly parallel 
to the body, and the elbow points backwards, the antibrachium 
downwards, and the manus backwards ; the pre-axial surface of 
the whole limb with the radius and pollex now faces outwards, 
and the postaxial surface with the ulna and fifth finger now faces 

1 This account is based on Chapter XX. of Flower's Osteology of the 
Mammalia. London 1876. 



INTRODUCTORY. POSITIONS OF THE LIMBS. 29 

inwards. In the Walrus and, to a certain extent, in the Sea- 
lions the anterior limb remains throughout life in this position. 
The posterior limb is also rotated, but the rotation in this 
case takes place forwards, so that the thigh lies nearly parallel 
to the body, the knee-joint pointing forwards ; the eras down- 
wards and the pes forwards. The pre-axial surface of the 
whole limb with the tibia and hallux looks towards the middle 
of the body, the postaxial surface with the fibula and fifth toe 
looks outwards. This is the position in which the hind limb 
is carried in nearly all mammals. 

In nearly all mammals a further change takes place in the 
position of the anterior limb. The radius and ulna have 
hitherto been parallel to one another, but now the lower end 
of the radius, carrying with it the manus, comes to be rotated 
forwards round the ulna, so that the manus, as well as the 
>mes to be forwardly-directed, and its pre-axial surface 
faces inwards. 

In the majority of mammals the radius and ulna are per- 
manently fixed in this, which is known as the prone position, 
but in man and some other mammals the manus can be 
pronated or turned into this position at will. When the 
radius and ulna are parallel throughout their whole length 
the manus is said to be in the supine position. 

The extensor side of a limb is that to which the muscles 
which straighten it are attached, the flexor side is that to 
which the muscles which bend it are attached. 



CHAPTER II. 
CLASSIFICATION. 

THE following classification includes only the forms 
mentioned in the succeeding pages. The relative value of 
some of the terms employed in classification is not identical 
throughout the book. This remark applies specially to the 
term group, which is a convenient one, owing to its not having 
such a hard and fast zoological meaning as has the term family, 
for instance. The term group is applied in this book to 
divisions of the animal kingdom of very different classificatory 
importance. 

PHYLUM CHORDATA. 

SUBPHYLUM A. HEMICHORDATA. 

Balanoglossus. 

Cephalodiscus. 

Rhabdopleura. 

? Phoronis. 

(? Actinotrocha larval Phoronis). 

SUBPHYLUM B. UROCHORDATA (TUNICATA). 
Group LARVACEA and others. 

SUBPHYLUM C. CEPHALOCHORDATA. 

Amphioxus laricelet. 

NOTE. In this chapter all the generic names printed in italics are 
those of extinct animals. 



CLASSIFICATION. 31 

SUBPHYLUM D. VERTEBRATA. 

DIVISION (I). CYCLOSTOMATA. 

Order 1. MARSIPOBRANCHII. 

Family Myxinoidei. Myxine hag-fish. 

Bdellostoma. 
Family Petromyzontidae. Petromyzon lamprey. 

(Ammocoetes larval lamprey.) 
Family Palaeospondylidae. Palaeospondylus. 

Order 2. OSTRACODEKMI. 

Suborder 1. HETEROSTRACI. 
Family Pteraspidae. Pteraspis. 

Suborder 2. OSTEOSTRACI. 
Family Cephalaspidae. Cephalaspis. 

Suborder 3. ANTIARCHA. 
Family Asterolepidae. Pterichthys. 
Asterolepis. 

DIVISION (II). GNATHOSTOMATA. 

A. ICHTHYOPSIDA. 

CLASS I. PISCES. 

Order 1. ELASMOBRANCHII. 
Suborder (1). ICHTHYOTOMI. 
Family Pleuracanthidae. Xenacanthus. 
Suborder (2). PLEUROPTERYGII. 

Cladoselache. 
Suborder (3). SELACHII. 

Group SQUALIDAE. 

Family Notidanidae. Heptanchus. 
Hexanchus. 

Chlamydoselache frill-gilled shark. 
Family Cochliodontidae. Cochliodu*. 



32 THE VERTEBRATE SKELETON. 

Family Cestraciontidae. Cestracion Port Jackson 

shark. 
Acrodus. 

Family Scylliidae. Scyllium spotted dog-fish. 
Family Lamnidae. Odontaspis. 
Family Carcharidae. Galeus tope. 
Family Spinacidae. Acanthias spiny dog-fish. 

Scymnus. 
Family Squatinidae. Squatina (Rhina) angel fish. 

Group BATOIDEI. 

Family Pristidae. Pristis saw-fish. 
Family Raiidae. Raia skate. 
Family Myliobatidae. Myliobatis eagle ray. 
Family Trygonidae. Trygon sting ray. 
Family Torpedinidae. Torpedo electric ray. 

Suborder (4). ACANTHODII. 
Family Acanthodidae. Acanthodes. 
Family Diplacanthidae. Diplacanthus. 

Order 2. HOLOCEPHALI. 

Family Chimaeridae. Chimaera rabbit fish. 
Harriotta. 
Callorhynchus. 
Ischyodus. 

Order 3. GANOIDEI. 
Suborder (1). GHONDROSTEI. 
Family Palaeoniscidae. Palaeoniscus. 

Trissolepis. 
Family Acipenseridae. Acipenser sturgeon. 

Scaphirhynchus. 

Family Polyodontidae. Polyodon (Spatularia) spoon- 
beaked sturgeon. 
Psephurus slender-beaked sturgeon. 



CLASSIFICATION. 33 

Suborder (2). CROSSOPTERYGII. 
Family Holoptychiidae. Holoptychius. 
Family Rhizodontidae. Rhizodus. 
Family Osteolepidae. Osteolepis. 
Family Polypteridae. Polypterus bichir. 

Calamoichthys reed-fish. 

Suborder (3). HOLOSTEI. 

Family Lepidosteidae. Lepidosteus gar pike. 
Family Semionotidae. Lepidotus. 
Family Amiidae. Amia bow-fin. 

Order 4. TELEOSTEI. 

Suborder (1). PLECTOGXATHI. 
Family Balistidae. Balistes file-fish. 
Family Gymnodontidae. Diodon globe-fish. 
Family Ostracionidae. Ostracion -coffer-fish. 

Suborder (2). PHYSOSTOMI. 
Family Siluridae cat-fishes. 
Family Cyprinidae. Cyprinus carp. 
Family Esocidae. Esox pike. 
Family Salmonidae. Salmo salmon. 
Family Clupeidae. Clupeus herring. 

Exocaetus 'flying fish'. 
Family Muraenidae. Anguilla eel. 

Suborder (3). ANACANTHIXI. 

Family Gadidae. Gadus cod, haddock, whiting. 
Family Pleuronectidae. Solea sole. 

Suborder (4). PHAKYXGOGXATHI. 
Family Labridae. Labrus wrasse. 

Scarus parrot fish. 
R. 3 



34 THE VERTEBRATE SKELETON. 

Subordei (5). ACANTHOPTERYGII. 

Family Cataphracti. Dactylopterus flying gurnard. 
Family Percidae. Perca perch. 

Order 5. DIPNOI. 
Suborder (1). SIRENOIDEI. 
Family Dipteridae. Dipterus. 

Family Monopneumona. Ceratodus barramunda. 
Family Dipneumona. Protopterus African mud-fish. 

Lepidosiren. 

Suborder (2). ARTHRODIRA. 
Family Coccosteidae. Coccosteus. 
Dinichthys. 

NOTE. Palaeontological research has disclosed the existence of a great 
number of forms which seem to connect with one another almost all the 
orders of fishes as usually recognised. Forms connecting the living 
Ganoids with the Teleosteans have been especially numerous, so that 
these terms Ganoid and Teleostean can hardly be any longer used in a 
precise and scientific sense. This has rendered the subject of the classifi- 
cation of fishes a very difficult one. Though unsuitable for adoption in 
a work like the present, by far the most natural classification hitherto 
proposed seems to be that of Smith Woodward 1 . He considers that the 
course of development of fishes has followed two distinct lines, the auto- 
stylic and hyostylic (see p. 119), and groups the various forms as follows: 

HYOSTYLIC. AUTOSTYLIC. 

Subclass 1. ELASMOBKANCHII. Subclass 3. HOLOCEPHALI. 

1. Ichthyotomi. 1. (unknown). 

2. Selachii. 2. Chimaeroidei. 

3. Acanthodii. 3. (unknown). 
Subclass 2. TELEOSTOMI. Subclass 4. DIPNOI. 

1. Crossopterygii (Palaeozoic 1. Sirenoidei. 

and Mesozoic). 

2. Crossopterygii (Cainozoic). 2. (unknown). 

3. Actinopterygii. 3. Arthrodira. 

The primitive forms in each of these four subclasses have the fins 
archipterygia (see p. 127). 

1 A. Smith Woodward, Catalogue of Fossil Fishes in the British 
Museum, Part II., Introduction, p. xii. 



CLASSIFICATION. 35 

CLASS II. AMPHIBIA. 

Order 1. URODELA. 
Suborder (1). ICHTHYOIDEA. 
Group A. PEREXXIBRAXCHIATA. 
Family Menobranchidae. Menobranchus. 
Family Proteidae. Proteus olm. 
Family Sirenidae. Siren. 

Group B. DEROTREMATA. 

Family Amphiumidae. Megalobatrachus. 

Cryptobranchus (Menopoma). 
Amphiuma. 

Suborder (2). SALAMAXDRIXA. 

Family Salamandridae. Salamandra salamander. 

Molge newt. 
Onychodactylus. 
Amblystoma. 
(Siredon axolotl, larval Am- 

blystoma). 
Batrachoseps. 
Spelerpes (Gyrinopbilus). 

Order 2. LABYRIXTHODONTIA. 
Group Lepospondyli. Branchiosaurux. 
Group Temnospondyli. Archegosaurus. 

ITyntnia. 

E > i.ch irosaurug. 
Group Stereospondyli. Capitosaurus. 

Mastodonsaurus. 



Order 3. 
Family Caeciliidae. Siphonops. 
Epicrium. 

32 



36 THE VERTEBRATE SKELETON. 

Order 4. ANURA. 
Suborder (1). AGLOSSA. 
Family Xenopidae. Xenopus. 
Family Pipidae. Pipa Surinam toad. 

Suborder (2). PHANEROGLOSSA. 

Group ARCIFBRA. 
Family Discoglossidae. Discoglossus painted frog. 

Bombinator fire-bellied frog. 
Alytes midwife frog. 

Family Pelobatidae. Pelobates toad frog. 
Family Hylidae. Hyla green tree-frog. 
Family Bufonidae. Bufo toad. 

Docidophryne. 
Family Cystignathidae. Ceratophrys horned frog. 

Group FlRMISTERNIA. 

Family Ranidae. Rana common and edible frogs. 
Family Engystomatidae. Brachycephalus. 

B. SAUROPSIDA. 

CLASS I. REPTILIA 1 . 

Order 1. THEROMORPHA. 

Group Anomodontia. Dicynodon. 

Udenodon. 

Group Placodontia. Placodus. 
Group Pariasauria. Pariasaurus. 

Elginia. 

Group Theriodontia. Dimetrodon. 
Galesaurus. 
Cynognathus. 

1 This classification of reptiles is mainly based on that of Lydekker 
(Catalogue of Fossil Reptiles in the British Muxeniii) but in some respects 
that of von Zittel has been followed. 



CLASSIFICATION. 37 

Order 2. SAUROPTERYGIA. 
Family Mesosauridae. Jfesosaunts. 
Family Nothosauridae. Xothosatirus. 
Family Plesiosauridae. Plesiosaurus. 

Pliosaurus. 

Order 3. CHELONIA. 
Suborder (1). TRIOXYCHIA. 
Family Trionychidae. Trionyx snapping turtle. 

Suborder (2). CRYPTODIRA. 
Family Dennochelydidae. Dermochelys (Sphargis) 

leathery turtle. 

Family Chelonidae. Chelone green turtle. 
Family Chelydridae. Chelydra terrapin. 
Family Chersidae. Testudo tortoise. 
Suborder (3). PLETJRODIRA. 
Family Chelydae. Chelys. 

Order i. ICHTHYOSAURIA. 
Family Ichthyosauridae. Ichthyosaurus. 

Order 5. RHYXCHOCEPHALIA. 
Suborder (1). RHYXCHOCEPHALIA VERA. 
Family Sphenodontidae. Sphenoclon (Hatteria). 
Family Rhynchosauridae. Hyperodapedon. 

Suborder (2). PROGAXOSAURIA. 
Family Proterosauridae. Proterosaunis. 

Order 6. SQUAMATA. 

Suborder (1). LACERTILIA. 

Group Lacertilia vera. 
Family Geckonidae. Gecko. 
Family Pygopodidae. Lialis scale-foot. 



38 THE VERTEBRATE SKELETON. 

Family Agamidae. Draco flying lizard. 

Agama. 

Family Iguanidae. Iguana. 
Family Anguidae. Ophisaurus (Bipes, Pseudopus). 

Anguis blind worm. 

Family Varanidae. Varanus monitor. 
Family Amphisbaenidae. Chirotes. 

Amphisbaena. 
Family Scincidae. Tiliqua (Cyclodus). 

Scincus -skink. 

Chalcides (Seps). 

Group Rhiptoglossa. 
Family Chamaeleonidae. Chamaeleon. 

Suborder (2). OPHIDIA. 

Family Typhlopidae. Typhlops blind snake. 
Family Boidae. Python. 

Family Colubridae. Tropidonotus ringed snake. 
Family Hydrophidae sea snakes. 
Family Crotalidae. Crotalus rattlesnake. 

Suborder (3). PYTHONOMORPHA. 
Family Mosasauridae. Mosasaurus. 

Order 7. DINOSAURIA. 
Suborder (1). SAUROPODA. 
Family Atlantosauridae. Brontosaurus. 
Family Cetiosauridae. Morosaurus. 

Suborder (2). THEROPODA. 

Family Megalosauridae. Megalosaurus (Ceratosaurus). 
Family Compsognathidae. Compsognathus. 



CLASSIFICATION. 

Suborder (3). ORTHOPODA. 

Section (a). STEGOSAURIA. 
Family Scelidosauridae. Polacanthus. 
Family Stegosauridae. Stegosaurus. 

Section (6). CERATOPSIA. 
Family Ceratopsidae. Polyonax (Ceratops). 

Section (c). ORNITHOPODA. 
Family Camptosauridae. Hypsilophodon. 
Family Iguanodontidae. Iguanodon. 
Family Hadrosauridae. Hadrosaurus. 

Order 8. CROCODILIA. 
Suborder (1). PARASUCHIA. 
Family Phytosauridae. Phytosaurus (Belodori). 

Suborder (2). EUSUCHIA. 

Family Teleosauridae. Teleosaurus. 

Metriorhynchus. 

Family Goniopholidae. Goniopholis. 
Family Alligatoridae. Alligator. 

Caiman. 

Jacare. 

Family Crocodilidae. Crocodilus. 
Family Garialidae. Garialis (Gavialis). 

Order 9. PTEROSAURIA. 

Family Pterodactylidae. Pterodactylus. 

Family Rhamphorhynchidae. Rhamphorhynchus. 

Family Pteranodontidae. Pteranodon. 



40 THE VERTEBRATE SKELETON. 

CLASS II. AVES 1 . 

Subclass (I). ARCHAEORNITHES. 
Archaeopteryx. 

Subclass (II). NEORNITHES. 

Order 1. RATITAE. 
Group .ffipyornithes. JZpyornis. 
Group Apteryges. Apteryx kiwi. 
Group Dinornithes. Moas. 
Group Megistanes. Casuarius cassowary. 

Dromaeus emeu. 

Group Rheornithes. Rhea American ostrich. 
Group Struthiornithes. Struthio ostrich. 

Order 2. ODONTOLCAE. 
Hesperornis. 

Order 3. CARINATAE. 

Group Ichthyornithiformes. 

Ichthyornis. 

Ap.atornis. 

Odontopteryx. 

Group Colymbiformes. 
Subgroup Colymbi divers. 

Group Sphenisciform.es. 

Subgroup Sphenisci penguins. 

1 This classification of birds is essentially that of Gadow and Selenka 
in Bronn's Classen und Ordnungen des Thier-reichs, Band vi., Abth. iv., 
Vogel. Leipzig, 1891. 



CLASSIFICATION. 41 

Group Ciconiiformes. 

Subgroup Steganopodes. Sula gannet 

Pelicanu s pelican. 
Phaethon frigate bird. 
Phalacrocorax cormorant. 

Subgroup Ardeae. Ardea heron 
Subgroup Ciconiae. Leptoptilus adjutant. 
Ciconia white stork. 

Group Anseriformes. 

Subgroup Palamedeae. Palamedea) 

I screamers. 
Chauna J 

Subgroup Anseres. Anas wild duck. 
Anser goose. 

Plectropterus -spur-winged goose. 
Cygnus swan. 
Mergus m erganser. 

Group Falconiformes. 

Subgroup Cathartae. Cathartes American vulture. 
Subgroup Accipitres. Falco falcon. 

Yultur vulture. 

Harpagus. 

Gypogeranus secretary bird. 

Group Tinamiformes. 

Subgroup Tinami. Tinamus. 

Group Galliformes. 

Subgroup Galli. Gallus fowl. 

Pa vo peacock . 
Subgroup Opisthocorni. Opisthocoruus hoatzin. 

Group Gruiformes. 

Gruidae cranes. 

Group Stereomithes. Phororhacos. 



42 THE VERTEBRATE SKELETON. 

Group Charadriiformes. 

Subgroup Limicolae. Charadriidae plovers. 

Parra j acana. 

Subgroup Lari. Laridae gulls. 
Alcidae auks. 

Subgroup Pteroclidae. Pterocles sandgrouse. 
Subgroup Columbidae. Columbae pigeons. 
Didus dodo. 
Pezophaps solitaire. 
Group Cuculiformes. 

Subgroup Cuculi. Scythrops. 

Subgroup Psittaci. Stringops owl-parrot. 

Group Coraciiformes. 

Subgroup Coraciae. Coracias roller. 

Buceros hornbill. 
Upu pa hoopoe. 
Subgroup Striges. Owls. 
Subgroup Cypseli. Cypselidae swifts. 

Trochilidae humming-birds. 
Subgroup Trogonidae. Trogons. 
Subgroup .Pici. Rhamphastos toucan. 
Picus woodpecker. 

Group Passeriformes. Crows, finches, larks, warblers, 

and many others. 

C. MAMMALIA 1 . 
Class MAMMALIA. 

Subclass (I). ORXITHODELPHIA or PROTOTHERIA. 
Order. MONOTREMATA. 

1 The classification adopted is almost entirely that given in Flower 
and Lydekker's Mammals Living and Extinct. London, 1891. 



CLASSIFICATION. 

Family Ornithorhynchidae. Ornithorhynchus duck- 
bill. 

Family Echidnidae. Echidna spiny anteater. 
Group Multituberculata. Tritylodon. 

Subclass (II). DIDELPHIA or METATHERIA. 

Order. MARSUPIALIA. 
Suborder (1). POLYPROTODOKTIA. 
Family Amphitheriidae. Phascol other bun. 
Family Didelphyidae. Didelphys opossum. 
Family Dasyuridae. Thylacinus Tasmanian wolf. 
Sarcophilus Tasmanian devil. 
Dasyurus. 

Family Peramelidae. Perameles bandicoot. 
Choeropus. 

Family Notoryctidae. Notoryctes marsupial mole. 

Suborder (2). DIPROTODONTIA. 
Family Phascolomyidae. Phascolomys wombat. 

Family Phalangeridae. Tarsipes. 

Phalanger cuscus. 

Phascolarctus koala. 

T/tylacoleo. 

Family Diprotodontidae. Diprotodon. 
Family Nototheriidae. Xototherium. 
Family Macropodidae. Macropus kangaroo. 
Family Epanorthidae. Coenolestes. 

Subclass (III). MONODELPHIA or EUTHERIA. 

Order 1. EDENTATA. 

Family Bradypodidae. Bradvpus ( 

n , , sloths. 

CholoepusJ 



44 THE VERTEBRATE SKELETON. 

Family Megatheriidae. Megatherium ground sloth. 
Family Myrmecophagidae. Myrmecophaga great ant- 
eater. 

Cycloturus two-toed ant- 
eater. 

Family Dasypodidae. Chlamydophorus\ 
Dasypus 
Priodon -armadillos. 

Tatusia 

Family Glyptodontidae. Glyptodon. 
Family Manidae. Manis pangolin. 
Family Orycteropodidae. Orycteropus aard .vark. 

Order 2. SIRENIA. 

Family Manatidae. Mauatus manatee. 
Family Rhytinidae. Rhytina Steller's sea-cow. 
Family Halicoridae. Halicore dugong. 
Family Halitheriidae. Halithenum. 

Order 3. CETACEA. 
Suborder (1). ABCHAEOCETI. 
Family Zeuglodontidae. Zeuglodon. 

Suborder (2). MYSTACOCETI or BALAENOIDEA. 
Family Balaenidae. Balaena right whale. 

Megaptera humpbacked whale. 
Balaenoptera rorqual. 

Suborder (3). ODONTOCETI. 
Family Physeteridae. Physeter sperm whale. 

Hyperoodon bottlenose. 

Ziphius. 

Mesoplodon. 
Family Physodontidae. Physodon. 



CLASSIFICATION. 45 

Family Squalodontidae. Squalodon. 
Family Platanistidae. Platanista Gangetic dolphin. 
Inia. 

Pontoporia. 
Family Delphinidae. Monodon narwhal. 

Phocaena porpoise. 

Orca killer. 

Globicephalus Ca'ing whale. 

Grampus. 

Lagenorhynchus. 

Delphinus dolphin. 

Tursiops. 

Prodelphinus. 

Order 4. UXGULATA. 
Division A. UNGULATA VERA. 
Suborder (1). ARTIODACTYLA. 

Section (a). SUINA. 

Family Hippopotamidae. Hippopotamus. 
Family Suidae. Sus pig. 
Babirussa. 

Phacochaerus wart hog. 
Hyotheriviii. 
Family Cotylopidae. Cotylops (Oreodori). 

Cyclopidius. 

Family Agriochoeridae. Agriochoerus. 
Family Anoplotheriidae. Anoplotherium. 

Section (6). TFLOPODA. 
Family Camelidae. Camelus cameL 
A uchenia llama. 

Section (c). TRAGULIXA. 

Family Tragulidae. Dorcatherium (Hyomoschus) 
chevrotain. 



46 THE VERTEBRATE SKELETON. 

Section (d). RUMINANTIA or PECORA. 
Family Cervidae. Moschus musk deer. 
Cervus deer. 
Cervulus muntjac. 
Hydropotes Chinese water deer. 
Family Giraffidae. Giraffa giraffe. 

Sivatherium. 

Family Antilocapridae. Antilocapra prongbuck. 
Family Bovidae. Tetraceros four-horned antelope. 
Gazella gazelle. 
Bos ox. 
Bison. 
Bubalus buffalo. 

Suborder (2). PERISSODACTYLA. 
Family Tapiridae. Tapirus tapir. 
Family Lophiodontidae. Lophiodon. 

Hyracotherium. 

Family Palaeotheriidae. Palaeotherium. 
Family Equidae. Hipparion. 

Equus horse. 
Family Rhinocerotidae. Rhinoceros. 

Elasmotherium, 
Family Titanotheriidae. TitanotJierium (Brontops). 

Palaeosyops. 

Family Chalicotheriidae. Chalicotherium. 
Family Macraucheniidae. Macrauchenia. 

Division B. SUBUNGULATA. 

Suborder (1). TOXODONTIA. 
Family Astrapotheriidae. Astrapotherium. 
Family Nesodontidae. Nesodon. 
Family Toxodontidae. Toxodon. 
Family Typotheriidae. Typotherium. 



CLASSIFICATION. 4-7 

Suborder (2). CONDTLARTHRA. 
Family Phenacodontidae. Phenacodus. 

Suborder (3). HYRACOIDEA. 
Family Hyracidae. Procavia (Hyrax). 

Suborder (4). AMBLYPODA. 
Family Coryphodontidae. Coryphodvn. 
Family Uintatheriidae. Uintatherium (Dinoceras). 

Suborder (5). PROBOSCIDEA. 
Family Dinotheriidae. Dinotherium. 
Family Elephantidae. Mastodon. 

Elephas elephan t . 

Group TILLODOXTIA. 

Order 5. RODEXTIA. 
Suborder (1). SIMPLICIDENTATA. 

Section SCIUROMORPHA. 
Family Castoridae. Castor beaver. 

Section MYOMORPHA. 
Family Lophiomyidae. Lophiomys. 
Family Muridae. Hydromys. 

Acanthomys spiny mouse. 
Mus mouse. 

Family Spalacidae. Bathyergus. 
Family Dipodidae. Dipus jerboa. 

Pedetes Cape jumping-hare. 

Section HYSTRICOMORPHA. 
Family Hystricidae. Hystrix porcupine. 
Family Chinchillidae. Chinchilla. 

Lagostomus viscacha. 



48 THE VERTEBRATE SKELETON. 

Family Dasyproctidae. Coelogenys paca. 

Dasyprocta agouti. 
Family Caviidae. Cavia guinea-pig. 

Hydrochaerus capybara. 

Suborder (2). DUPLICIDENTATA. 
Family Leporidae. Lepus hare and rabbit. 

Order 6. CARNIVORA. 
Suborder (1). CREODONTA. 
Family Hyaenodontidae. Hyaenodon. 

Suborder (2). CARNIVORA VERA or FISSIPEDIA. 
Section ^ELUROIDEA. 

Family Pelidae. Felis cat, lion, tiger. 

Machaerodus sabre-toothed lion. 
Family Viverridae. Viverra civet. 

Paradoxurus palm civet. 
Family Protelidae. Proteles aard wolf. 
Family Hyaenidae. Hyaena. 

Section. CYNOIDEA. 

Family Canidae. Canis dog, wolf, fox. 
Section ARCTOIDEA. 

Family Ursidae. Ursus bear. 
Family Mustelidae. Latax sea otter. 

Suborder (3). PINNIPEDIA. 
Family Otariidae. Otaria sea lion. 
Family Trichechidae. Trichechus walrus. 
Family Phocidae. Ogmorhinus sea leopard. 

Order 7. JNSECTIVORA. 
Suborder (1). DERMOPTERA. 
Family Galeopithecidae. Galeopithecus 'flying lemur'. 



CLASSIFICATION. 49 

Suborder (2). IXSECTIVORA VERA. 

Family Macroscelidae. Macroscelides jumping shrew. 
Family Erinaceidae. Erinaceus hedgehog. 

Gymnura. 

Family Soricidae. Sorex shrew. 
Family Talpidae. Talpa mole. 
Family Potamogalidae. Potamogale. 
Family Solenodontidae. Solenodon. 
Family Centetidae. Microgale. 

Centetes tenrec. 
Family Chrysochloridae. Chrysochloris golden mole. 

Order 8. CHIROPTERA. 

Suborder (1). MEGACHIROPTERA. 
Family Pteropidae. Pteropus flying fox. 

Suborder (2). MICROCHIROPTERA. 
Family Rhinolophidae. Horse-shoe bats. 
Family Phyllostomatidae. Desmodus vampire. 

Order 9. PRIMATES. 
Suborder (1). LEMUROIDEA. 
Family Tarsiidae. Tarsius tarsier. 
Family Chiromyidae. Chiromys aye aye. 

Suborder (2). AXTHROPOIDEA. 
Family Hapalidae. Hapale marmoset. 
Family Cebidae. Mycetes howling monkey. 

Ateles spider monkey. 

Family Cercopithecidae. Cynocephalus baboon. 

Macacus. 
Colobus. 

Family Simiidae. Hylobates gibbon. 
Simia orang. 
Gorilla. 

Anthropopithecus chimpanzee. 
Family Hominidae. Homo man. 
R. 4 



CHAPTER III. 

SKELETON OF HEMICHORDATA, UROCHORDATA, 
AND CEPHALOCHORDATA. 

SUBPHYLUM A. HEMICHORDATA. 

THE subphylum includes three genera, Balanoglossus^, Ce- 
phalodiscus and fihabdopleura; and perhaps a fourth, Phoronis. 

The skeletal structures found in Balanoglossus 2 are all 
endoskeletal. They include 

(1) The notochord. This arises as a diverticulum from 
the alimentary canal which grows forwards into the proboscis 
and extends beyond the front end of the central nervous 
system. It is hypoblastic in origin and arises in the same way 
as does the notochord of Amphioxus. Its cells become highly 
vacuolated and take on the typical notochordal structure 3 . The 
cavity of the primitive diverticulum becomes obliterated infront, 
but behind it opens throughout life into the alimentary canal. 

(2) The axial skeletal rods. These are a pair of chi- 
tinous rods which lie ventral to the notochord and in the collar 
region unite to form a single mass. 

(3) The branchial skeleton. The gill bars separating 
the gill slits from one another are strengthened by chitinous 
rods in a way closely similar to that in Amphioxus. But 
between one primary forked rod and the next there are two 
secondary unforked rods not one, as in Amphioxus. 

(4) The chondroid tissue. This is of mesoblastic origin 
and may be regarded as an imperfect sheath for the notochord. 

In Cephalodiscus and Rhabdopleura as in Balanoglossus 

1 The name Balanoglossus is used here in its widest sense to include 
all the Enteropneusta. 

2 See W. Bateson, Quart. J. Micr. Set. n. B. vol. xxrv. 1884, p. 208 and 
later; also E. W. Macbride, Ibid. vol. xxxvi. 1894, p. 385. 

3 See p. 52. 



SKELETON OF UROCHORDATA AND CEPHALOCHORDATA. 51 

the notochord forms a small diverticulum growing forwards 
from the alimentary canal into the proboscis stalk. 

Recent researches on Phoronis 1 show the existence in the 
collar region of the larva (Actinotrocha) of a paired organ, 
which is regarded by its discoverer as representing a double 
notochord. 

SUBPHYLUM B. UROCHORDATA (TUXICATA). 

Skeletal structures of epiblastic and hypoblastic origin 
occur in the Urochordata. Most Tunicates are invested by 
a thick gelatinous test which often contains calcareous spicules, 
and serves as a supporting organ for the soft body. The cells 
of this test are mesodermal in origin. 

In larval Tunicata and in adults of the group Larvacea 
the tail is supported by a typical notochord, which is confined 
to the tail. In all Tunicata except Larvacea all trace of 
the notochord is lost in the adult. 

SUBPHYLUM C. CEPHALOCHORDATA. 
This subphylum includes the well-known genus 




FIG. 3. DIAGRAM OF THE SKELETON OF Amphioxus lanceolatus x 3 
(after a drawing in the Index collection at the Brit. Mus.). 

1. skeleton of dorsal fin. o. branchial skeleton. 

2. notochord. 6. septa separating the myo 

3. neural tube. tomes. 

4. buccal skeleton. 7. skeleton of ventral fin. 

In Amjjkioxus the skeleton is very simple. It contains no 
trace of cartilage or bone and remains throughout life in a 

1 A. T. Masterman, P. R. Soc. Edinb. 189596, p. 59 ; and Anat. An:. 
1896, p. 266. 

2 See E. Ray Lankester, Quart. J. Micr. Sci. vol. xxix. n. s. 1889, p. 365. 
W. B. Benham, Ibid. vol. xxxv. n. s. 1893, p. 97. J. W. Kirkaldy, Ibid, 
vol. xxxvii. n. s. 1895, p. 303. The last-named writer divides the genus 
into three subgenera. 

42 



52 THE VERTEBRATE SKELETON. 

condition corresponding to a very early stage in Vertebrata. 
The skeleton of Amphioxus is partly hypoblastic, partly meso- 
blastic in origin. 

(a) Hypoblastic skeleton. 

The notochord (fig. 3, 2) is an elastic rod extending along 
the whole length of the body past the anterior end of* the 
nerve cord. It lies ventral to the nerve cord, and showsfno_ 
trace of segmentation. It is chiefly made up of greatly vacuo- 
lated cells containing lymph, but near the dorsal and ventral 
surfaces the cells are less vacuolated. The notochord is im- 
mediately surrounded by a structureless cuticular layer, the 
chordal sheath, and outside this comes the mesoblastic skeleto- 
genous layer, which also surrounds the nerve cord. 

The branchial skeleton. This consists of a series of 
chitinous elastic rods which strengthen the gill bars and are 
alternately forked and unforked ventrally. The forked rods 
are primary, and are U-shaped in section, the unforked rods 
are secondary, and are circular in section. All these rods are 
united at intervals by transverse rods. 

(6) Mesoblastic skeleton. 

The buccal skeleton. On each side of the mouth there 
is a curved bar resembling the notochord in structure. The 
bars are segmented, and each segment bears a smaller rod 
which supports a tentacle, the whole forming the buccal 
skeleton (fig. 3, 4). 

The notochord is enclosed in a thick sheath of connective 
tissue continuous with a thinner sheath round the nerve cord. 
The sheaths of the notochord and nerve cord together form the 
skeletogenous layer, and prolongations of it form the myomeres 
or septa between the myotomes or segments of the great lateral 
muscles of the body. 

The skeleton of each median fin consists of small 
cubical masses of a gelatinous substance arranged in rows 
(fig. 3, 1 and 7), and serving to strengthen the fins. 



CHAPTER IV. 

MpPHYLUM D. VERTEBRATA. 

THE animals included in this great group all possess au 
internal axial skeleton forming the vertebral column or back- 
bone : and a dorsal spinal cord. The vertebral column is 
developed from the skeletogenous layer, which surrounds the 
spinal cord together with the notochord and its sheath ; and 
in the great majority of cases the notochord becomes more or 
less modified and reduced in the adult. In some cases the 
notochord remains unmodified and the skeletogenous layer 
surrounding it is not segmented to form vertebrae, but in 
every case the neural arches which protect the spinal cord 
are segmented. The notochord never extends further forwards 
than the mid-brain. 

All true vertebrates possess a cranium or skeletal box 
enclosing the brain. 

(I.) CYCLOSTOMATA. 

The mouth in living forms is suctorial and is not supported 
by jaws. In some fossil forms the character of the mouth is 
unknown. 

Order I. MARSIPOBRAXCHII'. 

In these animals limbs and limb girdles are always com- 
pletely absent. They have no exoskeleton except horny teeth. 

The endoskeleton, excluding the notochord, is entirely 
cartilaginous or membranous. The axial skeleton consists of 
a cartilaginous cranium without jaws, succeeded bv a thick 

1 See W. K. Parker On the skeleton of the Marsipobranch fishes, 
Phil. Trans. 1883, London. 



54 THE VERTEBRATE SKELETON. 

persistent notochord enveloped in a sheath. The notochord 
in living forms is unsegmented, but segmented cartilaginous 
neural arches are present in some cases. A complicated series 
of cartilaginous elements occurs in relation to the mouth, gills, 
and sense organs. The median fins are supported by carti- 
laginous pieces, the radialia. The order includes the Lampreys 
and Hags. 

Order II. OSTRACODERMI 1 . 

The forms included in this group have long been extinct, 
being known only from beds of Upper Silurian and Lower 
Devonian age. They differ much from all other known animals. 
The exoskeleton is always greatly developed and includes 
(1) large bony plates covering the anterior region ; (2) scales 
covering the posterior region. The plates are deeply marked 
by canals belonging to dermal sense organs. Jaws are un- 
known, and arches for the support of the appendicular skeleton 
are rudimentary or absent. The tail is heterocercal (see p. 60). 

Suborder (1). HETEROSTRACI. 

The exoskeleton consists principally of calcifications form- 
ing dorsal and ventral shields which cover the head and ab- 
dominal region; the dorsal shield is formed of a few plates 
firmly united, the ventral shield of a single plate. The shields 
are composed of three layers, the middle layer being traversed 
by canals belonging to the dermal sense organs which open to 
the exterior by a series of pores. The tail is sometimes covered 
by scales. The orbits are widely separated and laterally 
placed. Paired appendages are absent. These curious forms 
are found in beds of Upper Silurian and Lower Devonian age. 
One of the best known genera is Pteraspis. 

Suborder (2). OSTEOSTRACI. 

The exoskeleton as in the Heterostraci consists of shields 
and scales, the shields being divisible into three layers. The 

1 See A. Smith Woodward, Catalogue of Fossil Fish in the British 
Museum, Part n., 1891. A. Smith Woodward, Nat. Sci. vol. i. 1892, 
p. 596. 



CYCLOSTOMATA. 55 

anterior part of the body is covered dorsally by a single large 
shield which differs from those of the Heterostraci in having 
the inner layer ossified. The middle layer contains canals for 
the passage of blood vessels, but the exoskeleton shows no 
impressions of dermal sense organs. The posterior part of the 
body is covered by large quadrangular scales. Paired append- 
ages are absent, but median dorsal and caudal fins occur 
supported by scales, not fin-rays. Cephalaspis, the best known 
of these animals, occurs in beds of Lower Devonian age. 

Suborder (3). AXTIARCHA. 

The exoskeleton is formed of bony plates, the dorsal and 
ventral shields each consisting of several symmetrically arranged 
pieces. The tail may be covered with small scales or may be 
naked. The head is articulated with the trunk, and its angles 
are drawn out into a pair of segmented paddle-like append- 
ages, covered with dermal plates. The orbits are close together. 
A dorsal fin and traces of mouth parts occur in Pterichthys. 
but the endoskeleton is unknown. The best known forms 
Pterichthys 1 and Asterolepis occur in beds of Lower Devonian 
age. 

GENERAL ACCOUNT OF THE SKELETON* OF 

MARSIPOBRANCHII. 

The Marsipobranchii are worm-like animals. The living 
forms include two families, the Myxinoidei (Hags) genera 
Myxine and Bdellostoma and thePetromyzontidae (Lampreys). 
Three species of Petromyzon are known, P. jlui-iatilis, P. 
marinus and P. planeri. The larval forms were for* a long 
time thought to belong to a separate genus and were called 
Ammocoetes. 

The Myxinoids, although very highly specialised in their 
own way, are at distinctly a lower stage of development than 
the adult Lamprey, and come nearer to the larval Lamprey or 
Ammocoete. 

1 See R. H. Traquair, Ann. Xat. Hist., ser. 6, vol. n. 1888, p. 485. 



56 



THE VERTEBRATE SKELETON. 



SPINAL COLUMN. 

In Myxinoids and larval lampreys, the notochord is en- 
closed in a thick chordal sheath, in connection with which in 
the tail region there occur cartilaginous pieces forming neural 
arch elements. In the trunk region, however, no cartilage 
occurs in connection with the spinal column, the only cartilage 
present being that forming the radialia of the dorsal fin. On 
the other hand in most species of lamprey (Petromyzon} 
cartilaginous pieces forming imperfect neural arches (fig. 4, 
B, 13) are found lying in the tough skeletogenous layer dorsal 




FIG. 4. A, DORSAL ; B, LATERAL AND C, VENTRAL VIEW OF THE 
SKULL OF Petromyzon marinus x 1 (after PARKER). 



1. horny teeth. 8. 

2. labial cartilage. 9. 

3. anterior dorsal cartilage. 10. 

4. posterior dorsal cartilage. 11. 

5. nasal capsule. 

6. auditory capsule. 12. 

7. dorsal portion of trabeculae. 13. 



lateral distal mandibular. 
lingual cartilage, 
branchial basket, 
cartilaginous cup supporting 

pericardium, 
sheath of notochord. - 
neural plate. 



to the notochord, and extending throughout the whole length 
of the trunk and tail. Two of these pieces, which are probably 
homologous with the neural plates (see p. 72) of Elasmobranchs, 
occur to each neuromere, or segment as determined by the 



CYCLOSTOMATA. 57 

spinal nerves. The dorsal and caudal fins are supported by 
paired cartilaginous radialia which are connected proximally 
with the skeletogenous layer. 

THE SKULL. 

In Myxinoids the cranium is a mere cartilaginous floor 
without side walls or roof, and the trabeculae 1 end without 
growing forwards into cornua. In Lampreys the trabeculae 
grow forwards and send up plates of cartilage which meet 
above (fig. 4, 7 ) and form side walls and a roof for part of the 
brain case. In Lampreys a labial suctorial apparatus is well 
developed, including a large ring-like piece of cartilage (fig. 4, 2) 
which supports the oral funnel and bears a large armament of 
horny teeth. In Myxinoids on the other hand the labial 
skeleton is small and consists merely of barbels round the 
mouth. 

The olfactory organ of Myxinoids has a very curious 
skeleton. It is covered with a kind of grating of cartilage 
which is prolonged in front into a tube composed of a series of 
imperfect cartilaginous rings. In Lampreys the olfactory 
organ opens merely by a short membranous passage. In 
correlation with the small development of the labial suctorial 
apparatus in Myxinoids the lingual apparatus is very greatly 
developed. The tongue in Jfyxine has been said to 'dominate 
the whole body' (Parker). It is supported by a great median 
cartilaginous bar which when followed forwards first becomes 
bifid and still further forwards becomes four-cleft. 

The horny teeth in Myxinoids are chiefly borne on the 
very large supralingual apparatus. They form a double series 
arranged in the form of an arch. In Myxine there are seven 
large teeth and nine small ones on each side. In BdeUostoma 
the teeth of the two rows are more equal in size. In Bdello- 
stonw, and Myxine it has been shown that imperfect calcified 
teeth occur below the horny teeth. 
1 See p. 17. 



58 THE VERTEBRATE SKELETON. 

In Lampreys the lingual apparatus (fig. 4, C, 9) is well de- 
veloped, but not excessively so. It consists of a long median 
cartilaginous bar which ends in front with a semicircular piece 
of cartilage supporting the median part of the tongue. 

In both Myxinoids and Lampreys there is a complicated 
branchial basket apparatus, but while in Myxinoids the basket 
apparatus is interbranchial, formed deep within the head 
near the hypoblastic lining of the throat, in Lampreys it is 
extra -branchial and formed outside the head cavities (fig. 
4, 10). The two sides of the basket apparatus in Myxine are 
not symmetrical. In the interbranchial basket apparatus of 
Myxinoids the hyoid and first and second branchial arches 
can be recognised. Traces of the interbranchial skeleton of 
Myxinoids can be detected in Lampreys, and similarly in 
Myxinoids, there are indications of the extrabranchial skeleton 
of Petromyzon. The branchial basket in Lampreys forms at 
its posterior end a kind of cup which supports the pericardium 
(fig. 4, 11). 

A remarkable Cyclostome named Palaeospondylus 1 has re- 
cently been described from the Scottish Old Red Sandstone. 
It differs however from all living Cyclostomes, in having a 
spinal column formed of distinct vertebrae with well-developed 
neural arches. The caudal fin is well developed and the dorsal 
radialia are forked as in lampreys. The skull is well calcified 
and the auditory capsules are specially large. The mouth is 
very similar to that of lampreys, being circular and without 
jaws ; it is provided with barbels or cirri. ' There is no trace 
of limbs and the average length is only about 1 \\ inches. 

1 R. H. Traquair, Ann. Nat. Hist. vol. vi. 1890, p. 485 ; P. Phys. Soc. 
Edinb. vol. xn. 189293, pp. 8794, and 312320. A. Smith Woodward, 
Nat. Sci. vol. in. p. 128, 1893. 



CHAPTER V. 
(II.) GNATHOSTOMATA. 

THE mouth is supported by definite jaws. 

ICHTHYOPSIDA. 

The epiblastic exoskeleton is generally unimportant, the 
mesoblastie exoskeleton is usually well developed. 

The notochord with its membranous sheath (1) may remain 
unmodified, or (2) may be replaced by bone or cartilage derived 
from the skeletogenous layer, or (3) may be calcified to a 
varying extent. 

The first vertebra is not homologous throughout the whole 
series and so is not strictly comparable to the atlas of Saur- 
opsids and Mammals. 

The centra of the vertebrae have 110 epiphyses. The 
skull may be (a) incomplete and membranous, or (6) more or 
less cartilaginous, or (c) bony. Membrane bones are not 
included in the cranial walls, and there are large unossified 
tracts in the skull. When membrane bones are developed in 
connection with the skull, a large parasphenoid occurs. The 
basisphenoid is always small or absent. The skull may be 
immovably fixed to the vertebral column, or may articulate 
with it by a single or double occipital condyle. When the 
occipital condyle is double, it is formed by the exoccipitels, 
and the basi-occipital is small or unossitied. The mandible 
may be (a) cartilaginous, (b) partially ossified, or (c) membrane 
bones may be developed in connection with it, if so, there is 



60 THE VERTEBRATE SKELETON. 

usually more than one membrane bone developed in connection 
with each half. 

There are at least four pairs of branchial arches present 
during development. The sternum, if present, is not costal 
in origin. 

CLASS I. PISCES. 

The exoskeleton is in the form of scales, which may be 
entirely mesoblastic or dermal in origin (e.g. cycloid and 
ctenoid scales), or may be formed of both mesoblast and epi- 
blast (e.g. placoid and ganoid scales). Large bony plates may 
be derived from both these types of scale. In general fish 
with a greatly developed dermal armour have the endoskeleton 
poorly developed; and the converse also holds good. 

The integument of the dorsal and ventral surfaces is 
commonly prolonged into longitudinal unpaired fins, sup- 
ported by an internal skeleton. These fins are distinguished 
according to their position as dorsal, caudal and anal fins. 
The dorsal and anal fins are used chiefly as directing organs, 
the caudal fin is however a most important organ of pro- 
pulsion. 

Three types of tail are found in fishes, viz. : 

1. The diphy cereal, in which the axis is straight and 
the tail is one-bladed and symmetrical, an equal proportion of 
radialia 1 being attached to the upper and lower surfaces of the 
axis. 

2. The heterocercal, in which the tail is asymmetrical 
and the axis is bent upwards, the proportion of radialia or of 
fin-rays attached to its upper surface being much smaller than 
that attached to its lower surface. 

3. The homocercal, in which the tail though ex- 
ternally symmetrical, so far resembling the diphycercal type, is 
internally really heterocercal, the great majority of the radialia 
or of the fin-rays being attached to the lower surface of the axis. 

1 See p. 79. 



PISCES. 61 

The cranium in the simplest cases (e.g. Selachii) forms a 
cartilaginous box enclosing the brain and sense organs ; in 
bony fishes it is greatly complicated. When palatine or 
pterygoid bones are present they are formed by the ossifi- 
cation of cartilage ; in Sauropsida and Mammalia they are 
laid down as membrane bones. There is no tympanic cavity 
or auditoiy ossicle in relation to the ear. 

There are two principal types of suspensorium by means of 
which the jaws are attached to the cranium : 

(1) The Autostylic. This is the primitive condition 
in which the mandibular arch articulates with the base of the 
cranium in front of the hyoid and in a similar manner. 

(2) The Hyostylic. In this case the mandibular arch 
becomes connected with the hyomandibular and supported by 
the hyoid arch. These terms are more fully discussed in 
Chapter VIII. 

There is always an internal framework supporting the 
gills ; it usually consists of the hyoid arch and five, rarely 
six or seven, pairs of branchial arches. The limbs are repre- 
sented by two pairs of tins, the pectoral and the pelvic ; they 
are not divided into proximal, middle and distal portions. The 
ribs do not unite with a median ventral sternum, or meet in 
the midventral line in any other way in the trunk region. 

Order I. ELASMOBRANCHII. 

The exoskeleton is in the form of placoid scales which are 
sometimes so numerous as to give the whole skin a rough 
surface forming shagreen. In some cases the placoid scales 
are enlarged to form plates or spines capped or coated with 
enamel. These spines may be imbedded in the flesh in front 
of the paired or unpaired fins, or may be attached to the tail. 
They are specially characteristic of the suborder Acanthodii. 
The endoskeleton is cartilaginous and true bone is never 
found. Much of the skeleton, especially of the vertebral 



62 THE VERTEBRATE SKELETON. 

column, is however often calcined, this being especially well 
seen in the anterior part of the vertebral column of Rays 
(Raiidae). In living forms cartilaginous biconcave vertebrae 
are always well developed, but in some extinct forms the 
notochord persists unconstricted. Neural and haemal arches 
are however always developed ; they sometimes remain 
separate, sometimes fuse with the centra. Ribs are often 
wanting and when present are often not separated off from the 
vertebrae. The cranium is a simple cartilaginous box whose 
most prominent parts are the capsules which enclose the 
sense organs. The skull is sometimes immovably fixed to 
the vertebral column, sometimes articulates with it by means 
of two condyles. There is no operculum and no representative 
of the maxilla or premaxilla. The teeth are very variable. 
Large pectoral and pelvic fins always occur. 

The Elasmobranchii may be divided into four suborders : 

(1) Ichthyotomi. 

(2) Pleuropterygii. 

(3) Selachii. 

(4) Acanthodii. 

Suborder (1). ICHTHYOTOMI 1 . 

The members of this suborder range from the Devonian to 
the Permian and so have long been extinct. 

The endoskeletal cartilage has granular calcifications evenly 
distributed throughout it. The notochord is unconstricted, but 
the neural and haemal arches are well-developed, and the 
neural spines are long and slender. There is a continuous 
dorsal fin with separate basalia and raclialia. The tail is di- 
phycercal, and the pectoral fins are typical archipterygia '-'. 
The pelvic fins of the male are prolonged to form claspers. 

1 For this aud other groups of extinct fish see A. Smith Woodward, 
' Catalogue of Fossil Fish in the British Museum, Parts i. in. Londou, 

188:) 95. 

2 See p. 127. i 



PISCES. ELASMOBRAXCHII. 63 

The best known of these primitive Elasmobranchs are the 
Pleu racan t hidae. 

Suborder (2). PLEUROPTERTGII. 

This suborder was formed for the reception of Cladoselache, 
an Elasmobranch found in the Lower Carboniferous of Ohio 1 . 

The exoskeleton is in the form of small, thickly-studded 
dermal denticles. The vertebral centra are unossified, and 
the tail is strongly heterocercal. There were certainly five, 
perhaps seven gill slits, and the suspensorium is apparently 
hyostylie. The paired fins are, according to the view which 
derives them by concentration from continuous lateral folds, 
the most primitive known (see p. 129) and claspers are 
absent . 

Suborder (3). SELACHII. 

Cartilaginous or partially calcified biconcave vertebrae are 
always well developed ; they constrict the notochord inter- 
vertebrally. The neural and haemal arches and spines are 
stout and intercalary cartilages (interdorsalia) are present. 
The tail is heterocercal, but in some cases (Squat ina) ap- 
proaches the diphycercal condition. In most cases the suspen- 
sorium is hyostylic, the jaws being attached to the cranium 
by means of the hyomandibular, and the palato-pterygo- 
quadrate bar not being fused to the cranium. There are 
generally five pairs of branchial arches, and gill rays are 
borne on the posterior surface of the hyoid arch, and on both 
the anterior and posterior surfaces of the first four branchial 
arches. The Xotidanidae differ from most Selachians in two 
respects, first as regards the suspensorium, Meckel's cartilage 
articulating directly with the palato-pterygo-quadrate bar, and 
not being connected with the hyoid arch ; and secondly as 
regards the number of branchial arches, six pairs occurring 
in Hexanchus and seven in Heptanchus. 

The pectoral fins are without the segmented axis of the 

1 See B. Dean, J. Uorphol. vol. ix. pp. 87 114, 1894, and Nat. Set. 
voL vni. p. 245, 1896. 



64 THE VERTEBRATE SKELETON. 

archipterygium. In most cases they are sharply marked off 
from the body and lie almost at right angles to it ; but in the 
Rays they have the form of lateral expansions in the same 
plane as the body, from which they are not sharply marked 
off. The pelvic fins in the male bear long grooved cartilaginous 
rods which are accessory copulatory organs or claspers. 

There are two principal groups of Selachii, the Squalidae 
or Sharks and Dogfish, and the Batoidei or Skates and Rays. 
The Squalidae have the shape of ordinary fish, the pectoral 
fins are vertically placed and the body ends in a powerful 
heterocercal tail. The Batoidei have flattened bodies owing 
to the great size and horizontal position of the pectoral fins. 
The tail is long and thin and is often armed with spines. 
The teeth in Selachii differ much in character in the different 
forms, and are always arranged in numerous rows. They are 
generally pointed and triangular or conical in the Squalidae, 
while in the Batoidei they are often broad and flattened. 

Suborder (4). ACANTHODII. 

The fishes included in this group are all extinct and 
in some respects are intermediate between Elasmobranchii 
and Ganoidei. The body is elongated and closely covered 
with small scales consisting of dentine enamelled at the sur- 
face. The notochord is persistent and the calcification of the 
endoskeletal cartilage is only superficial. The tail is hetero- 
cercal. The jaws bear small conical teeth, or in some cases 
are toothless. The skeleton of all the fins differs from that of 
modern Elasmobranchs in having the cartilaginous radialia 
much reduced, and the fins are nearly always each provided 
with an anterior spine, which except in the case of the pec- 
toral fins is merely inserted between the muscles. These spines 
are really enormous dermal fin-rays ; the pectoral fin-spine is 
articulated to the pectoral girdle. 

The suborder includes many well-known extinct forms like 
Acanthodes and Diplacanthus ; it ranges from the Devonian to 
the Permian. 



PISCES. HOLOCEPHALI. 



65 



Order II. HOLOCEPHALI. 
This order includes a single suborder only. 
Suborder. CHIMAEROIDEI. 

These singular tish have the skin smooth and in living 
forms almost or quite scaleless. The palato-pterygo-quadrate 
bar and hyomandibular are fused to the cranium, and Meckel's 
cartilage articulates directly with the part corresponding to the 
quadrate. The skull is distinctly articulated with the spinal 




FIG. 5. SKULL OF A MALE Chimaera monstrosa (after HUBBECHT). 



1. nasal capsule. 

2. cartilaginous appendage to 
the fronto-nasal region. 

3. erectile appendage. 

4. foramen by which the oph- 
thalmic nerves leave the orbit. 

5. foramen by which the oph- 
thalmic branch of the Yth nerve 
enters the orbit. 



6. auditory capsule. 

7. interorbital septum. 

8. mandible articulating with 
an outgrowth from the posterior 
part of the palato-pterygo-quadrate. 

9. teeth. 

10. labial cartilage. 
II. in. V. VII. IX. X. foramina 
for the passage of cranial nerves. 



column, the notochord is persistent and unconstricted, and the 
skeletogenous layer shows no trace of metameric segmentation, 



R. 



66 THE VERTEBRATE SKELETON. 

though in the neural arches this segmentation is readily trace- 
able. The neural arches of the first few vertebrae are fused 
together and completely surround the notochord, while they 
do not in other parts of the body. The tail is diphycercal. 
Of the living genera, in Callorhynchus there is no trace of 
calcification in the skeletogenous layer, while in Chimaera rings 
of calcification are found, there being three to five for each 
vertebra as indicated by the foramina for the exit of the spinal 
nerves. The pelvic fins are produced into claspers. Besides 
the living genera Chimaera, Harriotta and Callorhynchus a 
fair number of fossil forms are known, e.g. Ischyodus. 

Order 3. GANOIDBI. 

The fishes included under the term Ganoidei form a very 
heterogeneous group, some of which closely approach the Dipnoi, 
others the Elasmobranchii, others the Teleostei. The great 
majority of them are extinct, only eight living genera being 
known; these are all inhabitants of the northern hemisphere, 
and with the exception of Acipenser, which is both fluviatile 
and marine, are entirely confined to fresh water. 

The following is a list of the living genera of Ganoids with 
their respective habitats: 

Acipenser. Rivers and seas of the northern hemisphere. 

Scaphirhynchus. Mississippi and rivers of Central Asia. 

Polyodon (Spatularia). Mississippi. 

Psephurus. Yan-tse-kiang, and Hoangho. 

Polypterus. Rivers of tropical Africa. 

Calamqichthys. Some rivers of West Africa. 

Lepidosteus. Freshwaters of Central and North America 
and Cuba. 

Amia. Rivers of Carolina. 

The exoskeleton is very variable, thus the body may be : 

(a) Naked or with minute stellate ossifications as in 

the Polyodontidae. (6) Partially covered with large detached 



PISCES. GANOIDEI. 67 

bony plates as in Scaphirhynchus and Acipenser. (c) Entirely 
covered with rhomboidal ganoid scales as in Lepidosteus, 
Polypterus, Palaeoniscus and many extinct forms, (d) Covered 
with rounded scales shaped like the cycloid scales of Teleosteans 
as in Amia. (?) Having the trunk and part of the tail covered 
with rhomboidal scales, and the remainder of the tail with 
rounded scales as in Trissolepis. 

The teeth also are very variable. The endoskeleton shows 
every stage of transition from an almost entirely cartilaginous 
state as in Acipenser to a purely bony state as in Lepidosteus. 
Sometimes, as in Acipenser, the notochord persists, and its 
sheath is unsegmented ; sometimes, as in Lepidosteus, there 
are fully formed vertebrae. The tail may be heterocercal, as 
in Acipenser, or diphy cereal as in Polypterus. The cartila- 
ginous cranium is always covered with external membrane 
bone to a greater or less extent, and the suspensorium is 
markedly hyostylic. The pectoral girdle is formed of two 
parts, one endoskeletal and cartilaginous, corresponding with 
the pectoral girdle of Elasmobranchs, and one exoskeletal 
and formed of membrane bones, corresponding with the cla- 
vicular bones of Teleosteans. The pelvic tins are always 
abdominal. The fins often, as in Polypterus, have spines 
(fulcra) attached to their anterior borders. 

The order Ganoidei may be divided into three suborders : 

(1) CHONDROSTEI. Living genera Acipenser, Scaphi- 
rlit/itchus, Polyodon and Psephurus. 

(2) CROSSOPTERYGII. Living genera Polypterus and 
Calamoichthys. 

(3) HOLOSTEI. Living genera Lepidosteus and Amia. 

Suborder (1). CHOKDROSTEI. 

The skull is immovably fixed to the vertebral column. 
By far the greater part of the skeleton is cartilaginous. 
The notochord is persistent and unconstricted, its sheath is 
membranous, but cartilaginous neural and haemal arches are 

52 



68 THE VERTEBRATE SKELETON. 

developed. Intercalary pieces (interdorsalia) occur between 
the neural arches, and similar pieces (interventralia) between 
the haemal arches. The cranium is covered with membrane 
bone, and teeth are but slightly developed. The tail is hetero- 
cercal. Gill rays occur on the hyoid arch, and the gills are 
protected by a bony operculum attached to the hyomandi- 
bular. The skin (1) may be almost or quite naked, (2) may 
carry bony plates arranged in rows, or may be covered (3) with 
rhomboidal scales, or (4) partly with rhomboidal, partly with 
cycloidal scales. 

Suborder (2). CROSSOPTERYGII. 

The exoskeleton has the form of cycloidal or rhomboidal 
scales. The condition of the vertebral column differs in the 
different genera. Sometimes, as in Polypterus, there are well- 
developed ossified vertebrae; sometimes, as in many extinct 
forms, the notochord persists and is unconstricted. The tail 
may be diphycercal or heterocercal. The pectoral and some- 
times the pelvic fins consist of an endoskeletal axis bearing 
a fringe of dermal rays. 

Suborder (3). HOLOSTEI. 

The exoskeleton has the form of cycloidal or rhomboidal 
scales. The notochord is constricted and its sheath is seg- 
mented and ossified, forming distinct vertebrae, which are 
generally biconcave, sometimes opisthocoelous (Lepidosteus). 
The cartilaginous cranium is largely replaced by bone, and in 
connection with it we find not only membrane .bone, but 
cartilage bone, as the basi-occipital, exoccipitals, and pro-otic 
are ossified. The tail is heterocercal. The suspensorium 
resembles that of Teleosteans, consisting of a proximal ossifi- 
cation, the hyomandibular, which is movably articulated to 
the skull and a distal ossification, the symplectic. The two 
are separated by some unossified cartilage. The cartilaginous 
upper and lower jaws are to a great extent surrounded and 
replaced by a series of membrane bones. 



PISCES. TELEOSTEI. 69 

Order 4. TELEOSTEI. 

The exoskeleton is sometimes absent but generally consists 
of overlapping cycloid or ctenoid scales. Bony plates are some- 
times present, as in the Siluridae, or the body may be encased 
in a complete armour of calcified plates, as in Ostracion. 
Enamel is however never present, and the plates are entirely 
mesodermal. The skeleton is bony, but in the. skull much 
cartilage generally remains. The vertebral centra are usually 
deeply biconcave, and the tail is of the masked heterocercal 
type distinguished as homocercal. In the skull the occipital 
region is always completely ossified, while the sphenoidal 
region is generally less ossified. The skull has usually 
a very large number of membrane bones developed in connec- 
tion with it. The teeth vary much in character in the different 
members of the order, but are as a rule numerous and pointed, 
and are ankylosed to the bone. The suspensorium is hyo- 
stylic and the jaws have much the same arrangement as in 
the Holostei. There are five pairs of branchial arches, of 
which all except the last bear gill rays. A series of dermal 
opercular bones is developed in connection with these arches. 
The pectoral girdle consists almost entirely of dermal clavicular 
bones. The pelvic girdle has disappeared, its place being taken 
by the enlarged and ossified dermal fin-rays of the pelvic fins. 

The group includes the vast majority of living fish (see 
p. 33). 

Order 5. DIPNOI. 

The exoskeleton is of two types ; dermal bones are largely 
developed in the head region, while the tail and posterior 
part of the body may be naked or may be covered with over- 
lapping scales. The cranium remains chiefly cartilaginous, 
the palato-ptery go-quad rate bar is fused with the cranium, 
and the suspensorium is autostylic. The gill clefts are feebly 
developed and open into a cavity covered by an operculum. 
The notochord is persistent and unconstricted, and the limbs 
are archipterygia. The pelvic fins are without claspers. 



70 THE VERTEBRATE SKELETON. 

Suborder (1). SIRENOIDEI'. 

The head has well developed membrane bones. The trunk 
is covered with overlapping scales and bears no bony plates. 
Three pairs of teeth are present, two in the upper and one 
in the lower jaw, the two principal pairs of teeth are borne on 
the palato-pterygoids and splenials, while the third pair are 
found in the* vomerine region. The tail is diphycercal in 
living forms. In the extinct Dipteridae it is haterocercal. 
The pectoral girdle includes both membrane and cartilage 
bones. The pelvic girdle consists of a single bilaterally 
symmetrical piece of cartilage. 

This suborder is represented by the living genera Ceratodux, 
Protopterus and Lepidosiren, and among extinct forms by the 
Dipteridae and others. 

Suborder (2). ARTHRODIRA. 

Bony plates are developed not only on the head but also 
on the anterior part of the trunk, where they consist of a 
dorsal, a ventral, and a pair of lateral plates which articulate 
with the cranial shield. The posterior part of the trunk is 
naked. The tail is diphycercal. The jaws are shear-like, and 
their margins are usually provided with pointed teeth whose 
bases fuse with the tissue of the jaw and constitute dental 
plates. There seem to have been three pairs of these plates, 
arranged as in the Sirenoidei, the principal ones in the upper 
jaw being borne on the palato-pterygoids. Small pelvic fins 
are present, but pectoral fins are unknown. 

The Arthrodira occur chiefly in beds of Devonian and 
Carboniferous age. Two of the best known genera are 
Coccosteus from the European Devonian and Dinichthyx, a 
large predatory form from the lower Carboniferous of Ohio. 

1 A. Giinther, Phil. Trans, vol. 161, Part 11. 1871, p. 511. T. H. 
Huxley, "On Ceratodus and the classification of fishes," P.Z.S. 1876, 
p. 24. 



CHAPTER VI. 

THE SKELETON OF THE DOGFISH 1 . 
Scyllium canicula. 

I. EXOSKELETOX. 

The exoskeleton of the dogfish is mainly composed of placoid 
scales, each of which consists of a little bony base imbedded 
in the skin, bearing a small backwardly-directed spine formed 
of dentine capped with enamel. The scales are larger on 
the dorsal than on the ventral surface, and on the jaws they 
are specially large and regularly arranged in rows, there 
forming the teeth. The margins of the jaws or lips are with- 
out .scales. 

A second exoskeletal structure is found in the fins, all 
of which, both paired and unpaired, have, in addition to their 
cartilaginous endoskeleton, large numbers of long slender 
horny fibres, the fin-rays, which are of exoskeletal origin. 

II. EXDOSKELETOX. 

The endoskeleton of the dogfish consists almost entirely 
of cartilage, which however may become calcified in places, 
e.g. the centrum of each vertebra is lined by a layer of calcified 
tissue. 

The endoskeleton is divisible into an axial portion con- 
sisting of the vertebral column, skull, and skeleton of the 
median- fins, and an appendicular portion consisting of the 
skeleton of the paired fins and their girdles. 

1 See Marshall and Hurst's Practical Zoology, 4th ed. London, 189-5, 

p. -214. 



72 THE VERTEBRATE SKELETON. 

1. THE AXIAL SKELETON. 
A. THE VERTEBRAL COLUMN AND RIBS. 

The vertebral column consists of a series of some hundred 
and thirty vertebrae, each of which is united with its pre- 
decessor and successor in such a way as to allow a large 
amount of flexibility. 

These vertebrae are developed round an unsegmented 
rod, the notochord, which forms the axial support of the 
embryo. The notochord remains continuous throughout the 
whole vertebral column, but is greatly constricted opposite the 
middle of each vertebra, and thus rendered moniliform. The 
vertebrae are divided into two groups, an anterior group of 
trunk vertebrae, and a posterior group of caudal or tail 
vertebrae. 

A typical vertebra consists of a middle portion, the cen- 
trum, a dorsal portion, the dorsal or neural arch, which 
surrounds the spinal cord, and a ventral portion, the ventral 
or haemal arch, which similarly encloses a space. 

The tail vertebrae of the dogfish have this typical arrange- 
ment, the trunk vertebrae have the haemal arches modified. 

Each centrum is a short cylinder of cartilage surrounding 
an hourglass-shaped cavity occupied by the notochord. The 
neural arches are composed of three separate elements, the 
vertebral neural plates (basidorsalia), intervertebral 
neural plates (interdorsalia), and neural spines (supra- 
dorsalia). 

The vertebral neural plates are in the adult fused with 
their respective centra, and are notched behind for the exit 
of the ventral (motor) roots of the spinal nerves. The- inter- 
vertebral neural plates are polygonal pieces alternating 
with the vertebral neural plates ; they are notched behind, 
but at a more dorsal level than are the vertebral neural plates, 



THE SKELETON OF THE DOGFISH. THE SKULL. 73 

for the exit of the dorsal or sensory roots of the spinal 
nerves. 

The neural spines are small patches of cartilage filling 
up the gaps between the dorsal ends of the neural plates. 

The haemal arches (basiventralia) differ much in the 
trunk and tail portions of the vertebral column. In the 
trunk portion the centra are flattened below, and the two 
halves of the haemal arch diverge from one another as blunt 
ventri-lateral processes to which short cartilaginous rods, 
the ribs, are attached. Further back at about vertebra 37, 
the two halves of the haemal arch project downwards and 
meet forming a complete arch. Further back still, towards 
the hind end of the tail, the haemal arches bear median 
haemal spines (ventrispinalia). 

B. THE SKULL. 

The skull of the dogfish remains cartilaginous throughout 
the life of the animal, and has consequently a far more simple 
structure than have the skulls of higher animals, in which 
complication has been produced by the development of bone. 

The skull consists of the following parts : 

(1) a dorsal portion, the cranium, which lodges the brain, 
and to the sides of which the capsules of the auditory and 
olfactory sense organs are united. The cranium may be 
compared to an .unsegmented continuation of the vertebral 
column ; 

(2) a number of ventral structures, disconnected or only 
loosely connected with the cranium. These together con- 
stitute the visceral skeleton forming the jaws and sup- 
porting the gills. 

(1) THE CRANIUM. 

The Cranium is an oblong box, with a flattened floor and 
a more irregular roof. Its sides are expanded in front owing 



74 THE VERTEBRATE SKELETON. 

to the olfactory capsules, and behind owing to the auditory 
capsules, while in the middle they are deeply hollowed to form 
the orbits. 

(a) On the dorsal surface of the cranium the following 
points should be noticed. First at the anterior end, the large 
thin-walled nasal or olfactory capsules (fig. 6, 1), each of 
which is drawn out into a narrow cartilaginous process. 

The olfactory capsules have no ventral walls, and are 
separated from one another by the internasal septum, which 
is drawn out into a third slender process. . These three pro- 
cesses together constitute the rostrum (fig. 6, 2). 

Behind the olfactory capsules comes a large, nearly circular, 
hole, the anterior fontanelle, slightly behind which are the 
two ophthalmic foramina. The dorsal and ventral bound- 
aries of the orbits are respectively formed by the prominent 
supra-orbital and sub-orbital ridges. Behind are the audi- 
tory capsules (fig. 6, 8), each of which is marked by a pair 
of prominent ridges, converging towards the middle line to a 
pair of apertures. These apertures communicate with two 
canals, the aqueductus vestibuli, which lead into the in- 
ternal ear. The two ridges lodge respectively the anterior 
and posterior vertical semicircular canals of the ear. 

(6) The principal structures to be noted in a side view of 
the cranium are contained in the orbit or eye-cavity. Near the 
base of the orbit at its anterior end is seen the small orbito- 
nasal foramen (fig. 6, 7), for the passage of blood-vessels, 
not nerves. Above it is the large ophthalmic foramen 
(fig. 6, 5) so prominent in a dorsal view of the skull ; through 
it the ophthalmic branches of the fifth and seventh nerves 
pass. Slightly further back near the ventral surface is 
the large optic foramen (fig. 6, II.) for the passage of the 
second nerve. Vertically above the optic foramen, near the 
dorsal surface, is the very small foramen for the fourth 
nerve (fig. 6, IV.). Behind and a little above the optic 



THE SKELETON OF THE DOGFISH. THE SKULL. 75 

foramen is another small aperture, the foramen for the 
third nerve. Behind and slightly below this is the large 
foramen for the sixth and main branches of the fifth 
and seventh nerves (fig. 6, V.). In front of and slightly 




FIG. 6. LATERAL VIEW OF THE SKCLL OF A DOGFISH (ScyUium 
canicula) xf. 



1. nasal capsule. 

2. rostrum. 

3. interorbital canal. 

4. foramen for hyoidean artery. 

5. foramen for the exit of the 

ophthalmic branches of 
Vth and Vllth nerves. 

6. foramen through which the 

external carotid leaves the 
orbit. 

7. orbitonasal foramen. 

8. auditory capsule. 

9. foramen through which the 

external carotid enters the 
orbit. 



10. ethmo-palatine ligament. 

11. palato-pterygo-quadrate bar. 

12. Meckel's cartilage. 

13. hyomandibular. 

14. cerato-hyal. 

15. pharyngo-branchial. 

16. epi-branchial. 

17. cerato-branchiaL 

18. gill filaments, nearly all have 

been cut off short for the 
sake of clearness. 

19. extra-branchial. 

20. pre-spiracular ligament. 

II. III. IV. V. Va. Vila, foramina 
for passage of cranial nerves. 



below this foramen are seen two other small apertures; the 
more anterior and ventral of these (fig. 6, -t) is for the 
passage of a vessel connecting the efferent artery of the hyoid 
gill with the internal carotid artery inside the skull, the more 



76 THE VERTEBRATE SKELETON. 

posterior and dorsal is for the interorbital canal (fig. 6, 3) 
which unites the two orbital sinuses. Above and very slightly 
in front of the large foramen for the sixth and main parts 
of the fifth and seventh nerves, are two small foramina 
(fig. 6, Va., and Vila.), through which the ophthalmic 
branches of the fifth and seventh nerves enter the 
orbit. Behind and slightly below the large foramen just 
mentioned is a small hole through which the external carotid 
enters the orbit (fig. 6, 9). 

Behind the orbit is the auditory capsule. This is 
marked below by a prominent surface for the articulation 
of the hyomandibular, above which is the deep post- 
orbital groove for the passage of a blood-vessel, connecting 
the orbital and anterior cardinal sinuses. 

(c) Passing to the posterior end of the cranium : in the 
centre is seen the large foramen magnum through which 
the brain and spinal cord communicate. The notochord 
enters the skull just below this foramen, and on each side of 
the notochord is a projection, the occipital condyle, by 
which the first vertebra articulates with the skull. 

External to the condyles are the prominent pneumo- 
gastric foramina for the passage of the tenth nerves, and 
further to the sides, just beyond the posterior vertical semi- 
circular canals, are a pair of deep pits in which lie the 
foramina for the ninth nerves (fig. 6, IX.). 

(d) The broad and flat ventral surface of the cranium is 
continued in front as the inter-nasal septum and terminated 
laterally by the sub-orbital ridges. At a little behind the 
middle it is traversed by two shallow grooves along which 
the internal carotid arteries run. At the divergent ends of 
these grooves are seen two small apertures through which the 
external carotids enter the orbit (fig. 6, 9), and at the point 
where they meet is a single small aperture through which the 
internal carotid enters the cranium. 



THE SKELETON OF THE DOGFISH. VISCERAL SKELETON. 77 

THE ^VISCERAL SKELETON. 

The Visceral skeleton forms a series of seven cartilagi- 
nous arches or hoops, surrounding the anterior part of the 
alimentary canal, and enclosing a wide but rather shallow 
space. 

(a) The first or mandibular arch is the largest of the 
series, and forms the upper and lower jaws. Each half of the 
upper jaw or palato-pterygo-quadrate bar is formed by a 
thick cartilaginous rod which meets its fellow in the middle 
line in front, the two being united by ligament. Each half is 
connected to the cranium just in front of the orbit by the 
ethmo-palatine ligament (fig. 6, 10), and at its hind end 
articulates with one of the halves of the lower jaw. Each 
half of the lower jaw or Meckel's cartilage (fig. 6, 12) is 
a cartilaginous bar, wide behind but narrow in front, where 
it is united to its fellow by a median ligament. Imbedded 
in the tissue external to the upper jaw are a pair of 
labial cartilages, and a similar but smaller pair are 
imbedded in the tissue external to the lower jaw. 

The jaws are developed from a structure whose dorsal and 
ventral portions subsequently become of very different import- 
ance. The ventral portion forms both upper and lower jaws, 
the former being developed as an outgrowth from the latter. 
The dorsal portion forms only the prespiracular ligament 
(fig. 6, 20), a strong fibrous band containing a nodule of 
cartilage, and running from the anterior part of the auditory 
capsule to the point where the jaws are connected with the 
hvoinandibular. 

(b) The hyoid arch consists of a pair of cartilaginous 
rods which are attached at their dorsal ends to the cranium, 
and are united ventrally by a broad median plate of cartilage, 
the basi-hyal. Each rod is divided into a dorsal portion, 
the hyomandibular and a ventral portion, the cerato-hyal. 



78 THE VERTEBRATE SKELETON. 

The hyomandibular (fig. 6, 13) is a short stout rod of cartilage 
projecting outwards, and somewhat backwards and downwards 
from the cranium, with which it articulates behind the orbit 
and below the postorbital groove. Its distal end articulates 
with a rather long slender bar, the cerato-hyal (fig. 6, 14), 
which is in its turn attached to the side of the basi-hyal. The 
basi-hyal is a broad plate, rounded in front and drawn out 
behind into two processes to which the two halves of the 
first branchial arch are attached. The posterior surfaces of 
both hyomandibular and cerato-hyal bear slender cartilaginous 
processes, the gill rays. The hyoid arch forms the main 
suspensorium or means by which the jaws are attached to 
the cranium. This attachment is chiefly brought about by 
a series of short ligaments which connect the posterior ends 
of both upper and lower jaws with the hyomandibular, but 
there is also a ligament connecting the lower jaw with the 
cerato-hyal. The attachment of the jaws to the cranium is 
also partially effected by the prespiracular and ethmo-palatine 
ligaments. 

(c) Each of the five branchial arches is a hoop, in- 
complete above and formed of four or more pieces of cartilage. 
The most dorsal elements, the pharyngo-branchials, are 
flattened, pointed plates whose free inner ends run obliquely 
backwards, and terminate below the vertebral column. They 
are connected at their outer ends with the short broad epi- 
branchials (fig. 6, 1.6) which lie at the sides of the pharynx. 
From the epi-branchials arise the long cerato-branchials 
(fig. 6, 17) which run forwards and inwards along the ventral 
wall of the pharynx. The first four cerato-branchials are 
connected with small rods, the hypo-branchials, which run 
backwards to meet one another in the middle line. The last 
two pairs of hypo-branchials and the fifth cerato-branchials 
are connected with a broad median plate, the basi-branchial. 
Along the outer sides of the second, third and fourth cerato- 



THE SKELETON OF THE DOGFISH. MEDIAN FINS. 79 

branchials are found elongated curved rods, the extra- 
branchials (fig. 6, 19). The epi- branchials and cerato- 
branchials bear gill rays along their posterior borders. 

C. THE SKELETON OF THE MEDIAN Fixs. 

The dorsal fins have a skeleton consisting of a series of 
short cartilaginous rods, the basals or basalia, which slope 
obliquely backwards. Their bases are imbedded in the 
muscles of the back, while their free ends bear a number 
of small polygonal cartilaginous plates, the radials or radialia. 
Associated with this cartilaginous skeleton are a number of 
long slender horny fibres, the fin-rays, which have been already 
referred to in connection with the exoskeleton. The skeleton 
of the other median fins mainly consists of these fibres, the 
cartilaginous portion being reduced or absent 

2. THE APPENDICULAB SKELETON*. 

This includes the skeleton of the two pairs of limbs and of 

their respective girdles. 

THE PECTORAL GIRDLE forms a crescent-shaped hoop of 
cartilage, incomplete above and lying just behind the visceral 
skeleton. The midventral part of the hoop is the thinnest 
portion, and is drawn out in front into a short rounded process 
which is cupped dorsally and supports part of the floor of the 
pericardium (tig. 7, 1). On each side of this flattened mid- 
ventijal portion the arch becomes very thick and bears on its 
outer border a surface with which the three basal cartilages 
of the fin articulate. The dorsal ends or scapular portions 
of the girdle form a pair of gradually tapering horns. 

THE PECTORAL FIN articulates with the pectoral girdle by 
means of three basalia or basal cartilages, the pro-pterygium, 
meso-pterygium and meta-pterygium. The most anterior 
and the smallest of these is the pro-pterygium (fig. 7, 5), 



80 



THE VERTEBRATE SKELETON. 



while the most posterior one, the meta-pterygium (fig. 7, 3), 
is much the largest. Along the outer borders of the three 




FIG. 7. SEMIDOESAL VIEW OF THE PECTORAL GIKDLK AND FINS 

OF A DOGFISH (Scyllium canicula) x f . 
The gaps between the radialia are blackened. 

hollow in the midveiitral part 5. 

of the pectoral girdle which 6. 

supports the pericardium. 7. 

dorsal (scapular portion) of 8. 

pectoral girdle. 9. 
meta-pterygium. 
meso-pterygium. 



pro-pterygium. 
pro-pterygial radial, 
meso-pterygial radial, 
meta-pterygial radial, 
outline of the distal part of 

the fin which is supported 

by horny fin-rays. 



basalia are arranged a series of close set cartilaginous pieces, 
the radialia. The pro-pterygium supports only a single radial, 
which is however much larger than any of the others. The 
meso-pterygium also supports only a single radial which divides 
distally. 



THE SKELETOX OF THE DOGFISH. PELVIC GIRDLE. 81 

The meta-pterygium bears about twelve long narrow 
radials, the first nine of which are traversed by a transverse 
joint at about two-thirds of the way from their origin. Suc- 
ceeding the radials are a series of small polygonal pieces of 
cartilage arranged in one or more rows and attached to the ends 
of the radials, and finally the fin is completed by the dermal 
fin-rays. 




-3 



DORSAL VIEW OF THE PELVIC GIRDLE AND FINS OF A 
MAT.F. DOGFISH (Scyllium canicula). 



1. pelvic girdle. 

2. basi-pterygium. 



3. clasper. 

4. radialia. 



THE PELVIC GIRDLE is much smaller than the pectoral. 
It is formed of a stout nearly straight bar of cartilage placed 
transversely across the ventral region of the body. The bar 
has no dorsal or lateral extensions, and is terminated by short 
blunt processes. It bears on its posterior surface a pair of 
facets with which the pelvic fins articulate. 

THE PELVIC Fix is smaller and more simply constructed 
than is the pectoral. It consists of a long, somewhat curved 
R. 6 



82 THE VERTEBRATE SKELETON. 

rod, the basi-pterygium (fig. 8, 2), running directly backwards 
on the inner side of the fin, and articulating in front with the 
pelvic girdle. From its outer side arise a series of about 
fourteen parallel cartilaginous radials which bear smaller 
polygonal pieces. The anterior one or two of these radials may 
articulate independently with the pelvic girdle. In the adult 
male dogfish the distal end of the basi-pterygium bears a stout 
rod nearly as long as itself, and grooved on the dorsal surface. 
This is the skeleton of the clasper (fig. 8, 3). 



CHAPTER VII. 
THE SKELETON OF THE CODFISH 1 . (Gadus mvrrhua.) 

I. EXOSKELETOX. 

The exoskeleton includes 

(1) Scales. These are of the type known as cycloid 
and consist of flat rounded plates composed of concentrically 
arranged laminae of calcined matter, with the posterior margin 
entire. The anterior end of each scale is imbedded in the skin 
and is overlapped by the preceding scales. 

The teeth.. These are small, pointed, calcined struc- 
tures arranged in large groups on the premaxillae, mandible, 
vomer, and superior and inferior pharyngeal bones. 

(3) The fin-rays. These are delicate, nearly straight 
bony rods which support the fins. 

II. EXDOSKELETOX. 

The endoskeleton of the Codfish, though partially carti- 
laginous, is mainly ossified. 

It is divisible into an axial portion, including the skull, 
vertebral column, ribs, and skeleton of the median fins, and 
an appendicular portion, including the skeleton of the 
paired fins and their girdles. 

1. THE AXIAL SKELETON. 
A. THE VERTEBRAL COLUMN. 

This consists of a series of some fifty -two vertebrae, all com- 
pletely ossified. 

1 See T. J. Parker's Zootomy, London, 1884, p. 86. 

62 



84 THE VERTEBRATE SKELETON. 

It is divisible into two regions only, viz. the trunk region, 
the vertebrae of which bear movable ribs, and the caudal or 
tail region, the vertebrae of which do not bear movable ribs. 

Trunk vertebrae. 

These are seventeen in number; the ninth may be de- 
scribed as typical of them all. It consists of a short deeply 
biconcave centrum whose two cavities communicate by a 
narrow central canal. From the dorsal surface of the anterior 
half of the centrum arise two strong plates, the dorsal or 
neural processes, which are directed obliquely backwards 
and meet forming the dorsal or neural arch. This is pro- 
duced into a long backwardly - directed dorsal or neural 
spine. 

From the lower part of the anterior edge of each neural 
arch arise a pair of blunt triangular projections which over- 
hang the posterior half of the preceding centrum, and bear a 
pair of flattened surfaces which correspond to the anterior 
or pre-zygapophyses of most vertebrae, they differ however 
from ordinary pre-zygapophyses in the fact that they look 
downwards and outwards. From the posterior end of the 
centrum arise a pair of short blunt processes each of which 
bears an upwardly- and inwardly-directed articulating surface 
corresponding to a post-zygapophysis. 

The two halves of the ventral arch form a pair of large 
ventri-lateral processes which arise from the anterior half 
of the centrum and pass outwards and slightly backwards and 
downwards. 

Behind these there arises on each vertebra a second out- 
growth which is small and flattened, and like the ventri- 
lateral process serves to protect the air-bladder. The surface 
of the centrum is marked by more or less wedge-shaped de- 
pressions, one in the mid-dorsal line, and two on the ventral 
surface immediately mesiad to the bases of the ventri-lateral 
process. There are also a number of smaller depressions. 



THE SKELETON OF THE CODFISH. VERTEBRAE. 85 

The space between one centrum and the next is in the fresh 
skeleton filled up by the gelatinous remains of the notochord. 

The first few vertebrae differ from the others in having 
very short centra and no ventri-lateral processes. 

The first vertebra comes into very close relation to the 
ior part of the skull, articulating with the exoccipitals. 
In the next few vertebrae the centra gradually lengthen, 
and at the fourth or fifth vertebra the ventri-lateral pro- 
appear and gradually increase in size as followed back. 
They likewise gradually come to arise at a lower level on the 
centrum, and also become more and more downwardly directed, 
till at the last trunk vertebra they nearly meet. 

The neural spines of the anterior trunk vertebrae are 
much longer than those of the posterior ones, that of the first 
vertebra being the largest and longest of all, and articulating 
with the skull. The spinal nerves pass out through wide 
notches or spaces between the successive neural arches. 

Caudal vertebrae. 

The caudal vertebrae are about thirty-five in number, 
each consists of a centrum with a slender backwardly-directed 
dorsal or neural arch, similar to those of the posterior trunk 
vertebrae. The two halves of the ventral or haemal arch 
however do not form outwardly-directed ventri-lateral pro- 
but arise on the ventral surface of the centrum, and 
passing downwards meet and enclose a space ; they thus 
form a complete canal, and are prolonged into a backwardly- 
directed ventral or haemal spine. The anterior haemal 
arches are much larger than the corresponding neural arches, 
but when followed back they gradually decrease in size, till at 
about the twenty-fourth caudal vertebra they are nearly as 
small as the neural arches. The last caudal vertebra is suc- 
ceeded by a much flattened hypural bone or urostyle. which 
together with the posterior neural and haemal spines supports 
the tail-fin. 



86 THE VERTEBRATE SKELETON. 

B. THE RIBS. 

The ribs are slender, more or less cylindrical bones at- 
tached to the postero-dorsal faces of the ventri-lateral pro- 
cesses of all the trunk vertebrae except the first and second. 
The earlier ones are thicker and more curved ; the later ones 
thinner and more nearly straight. The ribs are homologous 
with the distal parts of the haemal arches of the caudal 
vertebrae. 

Associated with the ribs are a second series of rib-like 
bones, the intermuscular bones. These are slender, curved 
bones which arise from the ribs or from the ventri-lateral 
processes at a distance of about an inch from the centra, and 
curve upwards, outwards and backwards. In the anterior 
region where the ventri-lateral processes are short they arise 
from the ribs, further back they arise from the ventri-lateral 
processes. 

C. THE UNPAIRED OR MEDIAN FINS. 

These are six in number, three being dorsal, one caudal 
and two anal. 

The dorsal and anal fins each consist of two sets of 
structures, the fin-rays and the interspinous bones. Each 
fin-ray forms a delicate, nearly straight, bony rod which 
becomes thickened and bifurcated at its proximal or vertebral 
end, while distally it is transversely jointed and flexible, 
frequently also becoming more or less flattened. 

The first dorsal fin has thirteen rays, the second, sixteen to 
nineteen, the third, seventeen to nineteen. The first anal fin 
has about twenty-two, the second anal fourteen. In each 
fin the posterior rays rapidly decrease in size when followed 
back. 

The interspinous bones of the dorsal and anal fins 
alternate with the neural and haemal spines respectively, and 
form short, forwardly-projecting bones, each attached proxi- 
mally to the base of the corresponding fin-ray. 



THE SKELETON OF THE CODFISH. CAUDAL FIN. 87 

The caudal fin consists of a series of about forty-three 
rays which radiate from the posterior end of the vertebral 
column, being connected with the urostyle or hypural bone, 
and with the posterior neural and haemal spines without the 
intervention of interspinous bones. Like the other fin-rays 
those forming the caudal fin are transversely jointed, and are 
widened and frayed out distally. 

The tail-fin in the Cod is homocercal. i.e. it appears 
to be symmetrically developed round the posterior end of 
the vertebral column, though in reality a much greater pro- 
portion is attached below the end of the vertebral column than 
above it. It is a masked heterocercal tail. 

THE SKULL. 

Owing to the fact that very little cartilage remains in 
the skull of the adult Codfish, its relation to the completely 
cartilaginous skull of the Dogfish is not easily seen. Before 
describing it therefore, the skull of the Salmon will be de- 
scribed, as it forms an intermediate type. 

THE SKULL OF THE SALMON 1 . 

The Salmon's skull consists of (1) the chondrocranium, 
which remains partly cartilaginous and is partly converted 
into cartilage bone, especially in the occipital region, (2) a 
large series of plate-like membrane bones. 

THE CHONDROCRANIUM. 

This is an elongated structure, wide behind owing to the 
fusion of the large auditory capsules with the cranium, and 
elongated and tapering considerably in front ; in the middle 
it is much contracted by the large orbital cavities. 

DORSAL SURFACE OF THE CRANIUM. 

In the centre of the posterior end of the dorsal surface 
is the supra- occipital (fig. 9, A, 1) with a prominent posterior 

1 See W. K. Parker and G. T. Bettany, The Morphology of the Skull, 
London, 1877, chap. 3. 



88 



THE VERTEBRATE SKELETON. 




FlG. 9. A. DORSAL AND B. VENTRAL VIEW OF THE CRANIUM OF A SALMON 

(Salmo salar) from which most of the membrane bones have been 
removed (after PARKER). Cartilage is dotted. 



1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 
10. 
11. 



supra-occipital. 

epi-otic. 

pterotic. 

sphenotic. 

frontal. 

median ethmoid. 

parietal. 

lateral ethmoid. 

parasphenoid. 

vomer. 

exoccipital. 



1'2. opisthotic. 

13. alisphenoid. 

14. orbitosphenoid. 

16. foramen for passage of an 

artery. 

17. pro- otic. 

18. articular surface for hyo- 

mandibular. 

II. VII. IX. X. foramina for the 
passage of cranial nerves. 



THE SKULL OF THE SALMON. 89 

ridge. It is separated by two tracts of unossified cartilage 
from the large series of bones connected with the auditory 
organ. The first of these is the epi-otic (fig. 9, 2), which is 
separated by only a narrow tract of cartilage from the supra- 
occipital, and is continuous laterally with the large pterotic 
(tig. 9, A, 3) which overlaps in front a smaller bone, the 
sphenotic (fig. 9, 4). Both epi-otic and pterotic are drawn out 
into rather prominent backwardly-projecting processes. 

The greater part of the remainder of the dorsal surface 
is formed of unossified cartilage which is pierced by three 
large vacuities or fontanelles. The anterior fontanelle is 
unpaired, and lies far forward near the anterior end of the 
long cartilaginous snout, the two larger posterior one< lie 
just in front of the supra-occipital and lead into the cranial 
cavity. In front of the orbit the skull widens again,, and 
is marked by two considerable lateral ethmoid (fig. 9, 8) 
ossifi cations. In front of these are a pair of deep pits, the 
nasal fossae, at the base of which are a pair of foramina 
through which the olfactory nerves pass out : they communicate 
with a space, the middle narial cavity, seen in a longitu- 
dinal section of the skull. 

The long cartilaginous snout is more or less bifid in front, 
especially in the male (fig. 9). 

POSTERIOR END OF THE CRANIUM. 

The foramen magnum forms a large round hole leading 
into the cranial cavity, and is bounded laterally by the two 
exoccipitals and below by them, and to a very slight extent 
by the basi-occipital, the three bones together forming a 
concave occipital condyle by which the vertebral column 
articulates with the skull. 

The exoccipitals are connected laterally with a fourth 
pair of auditory bones, the opisthotics, and just meet the 
epi-otics dorsolaterally, while dorsally they are separated by a 
wide tract of unossitied cartilage from the supra-occipital. 

The opisthotics are connected laterally with the pterotics. 



90 



THE VERTEBRATE SKELETON. 



SIDE OF THE CRANIUM. 

At the posterior end is seen the basi-occipital in contact 
above with the exoccipital, which is pierced by a prominent 



10 



17 




FIG. 10. LATERAL VIEW OF 
salar) (after PARKER). 
Cartilage is dotted. 

1. supra-occipital. 

2. epi-otic. 

3. pterotic. 

4. opisthotic. 

5. exoccipital. 

6. basi-occipital. 

7. parasphenoid. 

8. sphenotic. 

9. alisphenoid. 

10. orbitosphenoid. 

11. lateral- or ectethmoid. 



THE CHONDROCRANIDM OF A SALMON (SdlmO 

A few membrane bones are also shown. 



olfactory pit ; the vomerine 
teeth are seen just below. 

pro-otic. 

basisphenoid. 

foramen for the passage of 
an artery. 

anterior fontanelle. 

posterior fontanelle. 



12. 

14. 
15. 

16. 

17. 
18. 

I. II. V. VII. IX. X. foramina 
for the passage of cranial nerves. 



foramen for the exit of the tenth nerve. In front of this lies 
a small foramen, sometimes double, for the ninth nerve. 

In front of the exoccipital is the large pro-otic pierced 
by two prominent foramina. Through the more dorsal of these 
(fig. 10, VII.) the facial nerve passes out, while the more 
ventral (fig. 10, 16) is for the passage of an artery. Dorsal to 
the exoccipital are the opisthotic and pterotic, and dorsal to 



THE SKULL OF THE SALMON. 91 

the pro-otic is the sphenotic. The pterotic is marked by a 
prominent groove often lined by cartilage, which is continued 
forwards along a tract of cartilage between the pro-otic and 
sphenotic. With this groove the hyomandibular articulates. 

There are considerable ossifications in the sphenoidal region 
of the side of the cranium. The anterior boundary of the pos- 
terior fontanelle is formed by the large alisphenoid, which 
is continuous behind with the pro-otic and sphenotic, and 
below with a slender basisphenoid. Both in front of and 
behind the basisphenoid there are considerable vacuities in the 
walls of the cranium ; through the posterior of these openings 
(fig. 10, V.) the main part of the trigeminal nerve passes out, 
and through the anterior one, the optic (fig. 10, II.). The 
alisphenoid is continuous in front with the orbitosphenoid 
(fig. 10, 10), which is pierced by the foramen for the exit of 
the first nerve (fig. 10, I.), and in front of the orbitosphenoid 
there is a large vacuity. The lateral ethmoid, is seen in the 
side view as well as in the dorsal view. Further forwards are 
seen the olfactory pits, and the long cartilaginous snout. 

A ventral view of the cartilaginous cranium shows much 
the same points as the side view. The basisphenoid appears 
on the surface immediately in front of the basi-occipital. 

THE SKULL WITH MEMBRAXE BOXES. 

The dorsal surface. The greater part of the dorsal 
surface in front of the supra-occipital is overlaid by a pair 
of large rough frontals (figs. 9, A, 5, and 10, 5). They cover 
the posterior fontanelles and stretch over from the sphenotic 
to the lateral ethmoid, forming a roof for the orbit. They 
meet in the middle line behind, but in front are separated 
by a narrow tract of unossified cartilage, and are overlapped 
by the median ethmoid (figs. 9, A, 6, and 11, 6). At the sides 
of the supra occipital behind the frontals are a pair of small 
parietals (tigs. 9, A, 7, and 11, 7). 

In a ventral view the cranium is seen to be chiefly 



92 



THE VERTEBRATE SKELETON. 



9 * r / / ; ! 

! ^ ^ n^~r J ' /' 




31 



FIG. 11. 



g: : ss 



LATEEAL VIEW OF THE SKULL OF A SALMON (Salmo salar) 
(after PAKKER). Cartilage is dotted. 



1. supra-occipital. 

2. epi-otic. 

3. pterotic. 

4. sphenotic. 

5. frontal. 

6. median ethmoid. 

7. parietal. 

8. nasal. 

9. lachrymal. 

10. sub-orbital. 

11. supra-orbital. 

12. cartilaginous sclerotic. 

13. ossification in sclerotic. 

14. meso-pterygoid. 

15. meta-pterygoid. 

16. palatine. 

17. jugal. 

18. quadrate. 



19. maxilla. 

20. premaxilla. 

21. articular. 

22. angular. 

23. dentary. 

24. hyomandibular. 

25. symplectic. 

26. epi-hyal. 

27. cerato-hyal. 

28. hypo-hyal. 

29. glosso-hyal. 

30. opercular. 

31. sub-opercular. 

32. infra-opercular. 

33. pre-opercular. 

34. supratemporal. 

35. branchiostegal rays. 

36. basi-branchiostegal. 



THE SKULL OF THE SALMON". 93 

covered by two large membrane bones, the parasphenoid 
(fig. 9, B, 9) behind, the -comer in front. A view of the 
posterior end differs from that of the cartilaginous cranium 
only in the fact that the end of the parasphenoid appears 
lying ventral to the basi-occipital. 

The lateral view differs very markedly from that of the 
cartilaginous cranium, there being a great development of 
membrane bone in connection with the jaws and branchial 
apparatus. Lying dorsally are seen the median ethmoid, frontal, 
parietal, and supra-occipital as before. Lying external to 
the middle of the median ethmoid is seen the small nasal 
(tig. 11, 8), and below the hinder part is the lachrymal. The 
lachrymal (tig. 11, 9) forms the first of a series of seven small 
bones which surround the orbit forming .the orbital ring. 
Of these the one lying immediately in the midventral line of 
the orbit is the sub-orbital, while the one lying in the mid- 
dorsal line and attached to the frontal is the supra-orbital 
(fig. 11, 11). The orbit has a cartilaginous sclerotic in which 
are two small ossifications (fig. 11, 13) laterally placed. 

BOXES OF THE UPPER JAW. 

The palato-pterygo-quadrate bar is in a very different 
condition from that of the dogfish, it is partially cartilaginous, 
partially converted into cartilage bone, partially overlapped by 
membrane bone. It is narrow in front but becomes much 
broader and deeper when followed back. Its anterior end forms 
the palatine which bears teeth, and in front is completely 
ossitied, while behind the cartilage is only sheathed by bone. 

Just behind the palatine the outer part of the cartilage is 
o->sitied, forming two small bones, the pterygoid and meso- 
pterygoid, while behind them is a larger, somewhat square 
bone, the meta-pterygoid (fig. 11, 15). 

Below the meta-pterygoid is a tract of unossified carti- 
lage, and then comes the quadrate (fig. 11, 18). 



94 THE VERTEBRATE SKELETON. 

The lower angle of the quadrate bears a cartilaginous con- 
dyle with which the mandible articulates. In front of the 
palatine the cartilaginous snout is overlapped by three mem- 
brane bones, the jugal, maxilla and premaxilla. 

The premaxilla (fig. 11, 20), the largest of these, overlaps 
the maxilla behind ; both bones bear teeth. Thzjugal (fig. 11, 
17) lies above the maxilla and overlaps it in front. 

THE LOWBE JAW. 

The lower jaw is a strong bar and is like the upper jaw, 
partly cartilaginous, forming Meckel's cartilage, partly ossi- 
fied, and sheathed to a considerable extent in membrane bone. 

The outer side and posterior end is ossified, forming the 
large articular (fig. 11, 21), but the condyle is cartilaginous 
and the anterior part of the articular forms merely a splint on 
the outer side of Meckel's cartilage, which extends beyond it 
for a considerable distance. The angle of the jaw just below 
the condyle is formed by a small angular (fig. 11, 22), and the 
anterior two-thirds of the jaw is sheathed in the large tooth- 
bearing dentary (fig. 11, 23). 

THE HYOID ARCH. 

The hyoid arch has a number of ossifications in it and is 
closely connected with the mandibular arch. 

The hyomandibular (fig. 11, 24) is a large bone which 
articulates with a shallow groove lined by cartilage and formed 
partly in the pterotic, partly in front of it. The hyomandibular 
is overlapped in front by the meta-pterygoid, while below it 
tapers and is succeeded by a small area of unossified cartilage 
followed by the forwardly-directed symplectic which fits 
into a groove in the quadrate. 

The unossitied tract between the hyomandibular and sym- 
plectic is continuous in front with a strong bar, which remains 
partly cartilaginous and is partly converted into cartilage 
bone. The proximal part is ossified, forming the epi-hyal, the 



THE SKULL OF THE SALMON*. 95 

middle part forms the cerato-hyal (fig. 11, 27), in front of 
which is the small hypo-hyal. The hyoid arches of the two 
sides are united by the large tooth-bearing glosso-hyal (fig. 11, 
29). Attached to the lower surface of the hyoid arch are a series 
of twelve flat branchiostegal rays (fig. 11, 35). Each overlaps 
the one in front of it, the posterior one being the largest. The 
branchiostegal rays of the two sides are united in front by an 
unpaired membrane bone, the basi-branekiostegal (fig. 11, 36). 

Opercular bones. Behind the hyomandibular there is a 
large bony plate, the operculum, formed of four large mem- 
brane bones. The anterior of these, the pre-opercular (fig. 11, 
33), is crescentic in shape, and with its upper end a small 
tupra-temporcU (fig. 11, 34) is connected. 

Behind the upper part of the pre-opercular is the largest of 
the opercular bones, the opercular proper. Its lower edge 
overlaps the sub-opercular, and both opercular and sub- 
opercular are overlapped by the infra-opercular (fig. 11, 32) 
in front. The infra-opercular is in its turn overlapped by 
the pre-opercular. 

BRANCHIAL ARCHES. 

There are five branchial arches, the first four of which 
bear gill rays. Each of the first three consists of a shorter 
upper portion directed obliquely backwards and outwards, 
and a longer lower portion forming a right angle with the 
upper and directed obliquely forwards and inwards. The 
greater part of each arch is ossified. 

The upper part of either of the first two consists of a short 
tapering pharyngo -branchial directed inwards, and of a 
long epi-branchial tipped with cartilage at both ends. The 
junction of the upper and lower parts is formed by a carti- 
laginous hinge-joint between the epi-branchial and cera to- 
branchial. The cerato-branchial is a long bony rod sepa- 
rated by a short area of cartilage from the hypo -branchial, 
which is succeeded by the basi-branchial meeting its fellow 



96 THE VERTEBRATE SKELETON. 

in the middle line. The fourth arch has a short epi-branchial 
and no ossified pharyngo-branchial, while the fifth is reduced 
to little more than the cerato-branchial, which bears a few 
teeth on its inner edge. All the branchial arches have pro- 
jecting from their surfaces a number of little processes which 
act as strainers. The first and fourth arches have one series 
of these, the second and third have two. 

THE SKULL OF THE CODFISH 1 . 

A full description having been already given of the Salmon's 
skull, that of the Codfish will be described in a briefer manner. 
The skull is very fully ossified, and the great number of plate- 
like bones render it a very complicated structure. 

THE CRANIUM. 

At the posterior end of the dorsal surface is the large 
supra-occipital, which is drawn out behind into the large 
blade-like occipital spine. On each side of the supra-occi- 
pital are the small irregular parietals, while in front of it the 
roof of the skull is mainly formed by the very large unpaired 
frontal. 

A complicated series of bones are developed in connection 
with the auditory capsule, which forms a large projecting 
mass united with the side of the cranium and drawn out be- 
hind into a pair of strong processes, the epi-otic and parotic 
processes. Both these processes are connected behind with a 
large V-shaped bone, the post-temporal (fig. 13, 1), which will 
be described when dealing with the pectoral girdle. The epi- 
otic process is formed by the epi-otic, which is continuous in 
front with the parietal. The parotic process is formed by 
two larger bones, a more dorsal one, the pterotic, and a more 
ventral and internal one, the opisthotic, which is continuous 
in front with the large pro-otic. Intervening between the 

1 T. J. Parker, Zootomy, London, 1884, p. 91. 



THE SKELETON OF THE CODFISH. THE SKULL. 97 

pterotic and frontal is another rather large bone, the sphenotic, 
this articulates below with the pro-otic. The pterotic and 
sphenotic together give rise to a large concave surface by 
which the hvomandibular articulates with the cranium. 
Several of the cranial nerves pass out through the bones of 
the auditory capsule. The ninth leaves by a foramen near 
the posterior border of the opisthotic, the fifth and seventh by 
a notch in the anterior border of the pro-otic. 

A number of bones are likewise developed in connection 
with the orbit forming the orbital ring. Of these the most 
anterior, the lachrymal, is much the largest, the others are 
five to seven in number, the most ventral being the suborbital. 
The sclerotic coat of the eye is cartilaginous. 

Two pairs of bones and one unpaired bone are developed in 
connection with the olfactory capsules, of these, the nasals 
are narrow bones lying next the lachrymals, but nearer the 
middle line : they overlap the second pair of bones, the ir- 
regular lateral ethmoids. These meet one another in the 
middle line, and are overlapped behind by the frontal. They 
articulate laterally with the lachrymal and palatine, and ven- 
trally with the parasphenoid. 

In a posterior view the foramen magnum and the four 
bones which surround it and together form the occipital seg- 
ment are well seen. On the ventral side is the basi-occipital, 
terminated posteriorly by a slightly concave surface which 
articulates with the centrum of the first vertebra. The sides 
of the foramen magnum are formed by the exoccipitals, a 
pair of very irregular bones, pierced by a pair of prominent 
foramina for the exit of the tenth nerves. The exoccipitals 
also bear a pair of surfaces for articulation with corresponding 
ones on the neural arch of the first vertebra. The most dorsal 
of the four bones is the supra- occipital. 

On the ventral surface of the cranium in front of the basi- 
occipital is seen the parasphenoid, a very long narrow bone 
which underlies the greater part of the cranium. Behind, it 
R. 7 



98 THE VERTEBRATE SKELETON. 

articulates dorsally with the basi-occipital and dorsolaterally 
with the pro-otics and opisthotics, in front it articulates 
dorsally with the lateral ethmoid and ventrally with the 
vomer. At the sides of the parasphenoid are the small ali- 
sphenoids articulating above with the postfrontals, in front 
with the frontals, and behind with the pro-otics. 

The vomer is an unpaired bone lying immediately in front 
of the parasphenoid. In front it terminates with a thickened 
curved margin bearing several rows of small teeth ; behind 
it tapers out into a long process which underlies the anterior 
part of the parasphenoid. Immediately dorsal to the vomer 
is another median bone, the median ethmoid; this is truncated 
in front and tapers out behind into a process which tits into a 
groove on the ventral side of the frontal. 

BONES IN CONNECTION WITH THE UPPER JAW. 

These bear a close resemblance to those of the Salmon. 
The most anterior bone is the premaxilla, a thick curved bone 
meeting its fellow in the middle line. The point of junction 
of the two is drawn out into a short process, and the oral 
surface is thickly covered with small teeth. The dorsal ends 
of the premaxillae are seen in the fresh skull to meet a large 
patch of cartilage. Behind the premaxilla is the maxilla, a 
long rod-like toothless bone, somewhat expanded at the upper 
end where it articulates with the premaxilla and vomer. 

Articulating in front with the anterior end of the maxilla 
and with the lateral ethmoid is a very irregular bone, the 
palatine (fig. 12, 1); it articulates behind with two flat 
bones, the pterygoid and meso-pterygoid. The ptery- 
goid is united behind with two more bones, the quadrate 
(fig. 1 2, 4) and meta-pterygoid. The quadrate is a rather 
stout irregular bone, bearing on its lower surface a promi- 
nent saddle-shaped articulating surface for the mandible. 
The palatine, pterygoid and quadrate bones are the ossified 



THE SKELETON OF THE CODFISH. UPPER JAW. 99 

representatives of the palato-ptery go-quad rate bar of the 
Dogfish. 




15 



FIG. 12. MANDIBULAR AND HTOID ARCHES OF A COD (Gadus 
morrhua) x (Brit. Mus.). 



1. palatine. 

2. meso-pterygoid. 

3. pterygoid. 

4. quadrate. 

5. symplectic. 

6. meta-pterygoid. 

7. hyomandibular. 

8. angular. 



9. articular. 

10. dentary. 

11. inter-hyal. 

12. epi-hyal. 

13. cerato-hyal. 

14. hypo-hyal. 

15. uro-hyal. 

16. branchiostegal rays. 



The quadrate is united behind with the symplectic 
(fig. 12, 5), and the meta-pterygoid with the symplectic and 
hyomandibular, both of which bones will be described im- 
mediately in connection with the hyoid arch. 

72 



100 THE VERTEBRATE SKELETON. 

THE LOWER JAW. 

The lower jaw or mandible like that of the Salmon is 
partly cartilaginous, forming Meckel's cartilage, partly 
formed of cartilage bone, partly of membrane bone. Meckel's 
cartilage is of course not seen in the dried skull. 

The lower jaw includes one cartilage bone, the articular 
(fig. 12, 9), this is a large bone connected by a saddle- 
shaped surface with the quadrate. Meckel's cartilage lies in 
a groove on its under surface, and projects beyond it in front. 
The angular is a small thick bone united to the lower surface 
of the articular at its posterior end. The dentary (fig. 12, 10) 
is a large tooth-bearing bone meeting its fellow in the middle 
line in front, while the articular fits into a deep notch at its 
posterior end. 

THE HYOID ARCH. 

The hyomandibular (fig. 12, 7) is a large irregular bone, 
articulating by a prominent rounded head with the sphenotic 
and pterotic. It is united in front with the meta-pterygoid 
and symplectic, and sends off behind a strong process which 
articulates with the opercular. The symplectic is a long 
somewhat triangular bone drawn out in front into a process 
which fits into a groove on the inner surface of the quadrate. 
The distal portion of the hyoid arch is strongly developed and 
consists of first the inter-hyal (fig. 12, 11), a short bony rod, 
which articulates dorsally with a patch of cartilage intervening 
between the posterior part of the hyomandibular and the sym- 
plectic. Below it is united with the apex of the triangular 
epi-hyal, a bone suturally connected with the large cerato- 
hyal (fig. 12, 13) which unites distally with two small hypo- 
hyals. To the cerato-hyal are attached a series of seven 
strong curved cylindrical rods, the branchiostegal roys. The 
first of these is the smallest and they increase in size up to the 
last. The four dorsal ones are attached to the outer surface 
of the cerato-hyal, the three ventral ones to its inner surface. 



THE SKELETON OF CODFISH. BRANCHIAL AECHES. 101 

Interposed between the hypo-hyals of the two sides is an 
unpaired somewhat triangular plate, the uro-hycd or basi- 
l>r<inchiosteyal (fig. 12, 15). 

THE BRANCHIAL ARCHES. 

The branchial arches are five in number and consist of 
the following parts on each side. The dorsal end is formed of 
the supra-pharyngeal bone, a large irregular bone covered 
vent rally with teeth of a fair size, and representing the fused 
pharyngo-branchials of the four anterior arches. Its external 
surface is continuous with four small epi-branchials which 
pass horizontally backwards and outwards. Their distal ends 
meet four long cerato-branchials which are directed for- 
wards and inwards and form the principal part of the arches. 

Each of the first three cerato-branchials articulates ven- 
t rally with a hypo-branchial, and the hypo-branchials of 
the two sides are united in the middle line by an unpaired 
basi-branchial. The third hypo-branchial is much flattened. 
The fourth cerato-branchial is united by cartilage with the 
posterior surface of the third hypo-branchial, which it meets 
near the middle line. 

The fifth arch consists only of the cerato-branchial, a wide 
-structure covered with teeth and generally called the inferior 
pharyngeal bone. 

The skeleton of the operculum consists of the same four 
bones as in the Salmon, namely the opercular, the infra- 
opereular, the pre-opercular and the sub-opercular. Of these 
the anterior bone, the pre-opercvlar, is the largest, while the 
infra-opercular is the smallest. The opercular has a facet for 
articulation with the hyomandibular. 

2. THE APPENDICULAR SKELETON*. 

THE PECTORAL GIRDLE. 

This is of a highly specialised type. Membrane bones are 
greatly developed, and the cartilage bones, the scapula and 
coracoid, are much reduced in size and importance. 



102 



THE VERTEBRATE SKELETON. 



The largest bone in the shoulder girdle is the clavicle 
(tig. 13, 3), which is irregularly crescent shaped, thick in front 




FIG. 13. THE EIGHT HALF OF THE PECTORAL GIRDLE AND RIGHT 
PECTORAL FIN OF A COD (Gadus morrhuo) x \ (Brit. Mus.). 
post-temporal. 5. scapula, 

supra-clavicle. 6. post-clavicle, 

clavicle. 7. bracbial ossicles, 

coracoid. 8. dermal fin-rays. 



and tapering off behind. To the outer side of its upper part 
is attached a thick cylindrical bone, the supra-clavicle, which 
passes upwards and is connected with a strong V shaped 
bone, the post-temporal. The apex of the V meets the supra- 
clavicle, the inner limb articulates with the epi-otic process, 
the outer with the parotic process. Projecting downwards from 
the upper part of the clavicle is a long bony rod, flattened 



THE SKELETON OF THE CODFISH. THE FINS. 103 

proximally and cylindrical and pointed distally, this is the 
post-clavicle (fig. 13, 6). 

The scapula (fig. 13, 5) is a small irregular plate of bone 
attached to the inner side of the middle of the clavicle. The 
coracoid 1 is a larger plate of similar character, irregularly 
triangular in shape, attached to the inner side of the clavicle 
immediately below the scapula. The scapula and coracoid 
bear the pectoral fin. 

THE PECTORAL FINS. 

Eacli of these consists of four small irregular bones, the 
brachial ossicles (fig. 13, 7), bearing a series of about nineteen 
dermal Jin-rays. The brachial ossicles represent the reduced 
and modified radialia and basalia of cartilaginous fish such as 
the dogfish. The fin-rays (fig. 13, 8) which form the whole 
external portion of the fin are long slender rods having 
essentially the same character as those of the unpaired fins. 

THE PELVIC GIRDLE. 

The pelvic girdle in the Cod as in other Teleosteans is 
entirely absent, its place being taken by the enlarged basi- 
pterygia of the fins. 

THE PELVIC FIXS. 

These have a very anomalous position in the Cod, being 
attached to the throat in front of the pectoral girdle. Each 
consists of a basal portion, the basi-pterygium, and of a 
number of dermal rays. The basi-pterygium consists of an 
expanded ventral portion which meets its fellow below in the 
middle line, and to which the rays are attached, and of an in- 
wardly-directed dorsal portion which also meets its fellow and 
is imbedded in the flesh. The rays are six in number and 
are long slender structures similar to those of the other fins. 

1 According to Or. Swirski, Schultergiirtel des Hechtts, Dorpat, 1880, 
the true coracoid is aborted, and the so-called coracoid of Teleosteans is 
really the precoracoid. 



CHAPTER VIII. 

GENERAL ACCOUNT OF THE SKELETON IN 
FISHES 1 . 

EXOSKELETON. 

The most primitive type of exoskeleton is that found in 
Elasmobranchs and formed of placoid scales; these are tooth- 
like structures consisting of dentine and bone capped with 
enamel, and have been already described (p. 4). In most 
Elasmobranchs they are small and their distribution is fairly 
uniform, but in the Thornback skate, Eaia clavata, they have 
the form of larger, more scattered spines. In adult Holo- 
cephali and in Polyodon and Torpedo there is no exoskeleton, 
in young Holocephali, however, there are a few small dorsal 
ossifications. 

The plates or scales of many Ganoids may have been 
formed by the gradual fusion of elements similar to these 
placoid scales, and often bear a number of little tooth -like, 
processes. In Lepidosteus, Polypterus, and many extinct 
species, these ganoid scales, which are rhomboidal in form 
and united to one another by a peg and socket articulation, 
enclose the body in a complete armour. In Trissolepis part of 
the tail is covered by rhomboidal scales, while rounded scales 
cover the trunk and remainder of the tail. Acipenser and 
Scaphirhynchus have large dermal bony plates which are not 
rhomboidal in shape and do not cover the whole body. In 

1 The following general works on fishes may be referred to : Bashford 
Dean, Fishes, Living and Fossil, New York, 1895. A. Giinther, An 
Introduction to tlie Study of Fishes, Edinburgh, 1880. A. A. W. Hubrecht 
and M. Sagemehl, Fische in Bronn's Classen uiid Ordnungen des Tliicr- 
reichs, Band vi. Leipzig, 1876. 



THE SKELETON IX FISHES. SCALES AND FIX-RAYS. 105 

Acipenser a single row extends along the middle of the back 
and two along each side. 

The majority of- Teleosteans have thin flattened scales 
which differ from those of Ganoids in being entirely meso- 
dermal in origin, containing no enamel. There are two prin- 
cipal types of Teleostean scales, the cycloid and ctenoid. A 
cycloid scale is a flat thin scale with concentric markings 
and an entire posterior margin. A ctenoid scale differs in 
having its posterior margin pectinate. The Dipnoi have over- 
lapping cycloid scales. The rounded scales of Amia and of many 
fossil ganoids such as Holoptychius are shaped like cycloid 
scales, but differ from them in being more or less coated with 
enamel. In Eels and some other Teleosteans the scales are 
completely degenerate and have almost disappeared. Some 
Teleosteans, like Diodon hystrix, have scales with triradiate 
roots from which arise long sharp spines directed backwards. 
These scales, which resemble teeth, contain no enamel ; they 
become erect when the fish inflates its body into a globular 
form. Many Siluroicls have dermal armour in the form of 
large bony plates which are confined to the anterior part 
of the body. In Ostracion the whole body is covered by 
hexagonal plates, closely united together. 

The fin-rays are structures of dermal origin which entirely 
or partially support the unpaired fins, and assist the bony 
or cartilaginous endoskeleton in the support of the paired fins. 

In Elasmobranchs, Dipnoi, and Chondrosteous ganoids the 
skeletons of the fins are, as a rule, about half of exoskeletal, 
half of endoskeletal origin, the proximal and inner portion 
Ijeing cartilaginous and endoskeletal, the distal and outer portion 
being exoskeletal, and consisting of horny or of more or less 
calcified fin-rays. In bony Ganoids and Teleosteans the endo- 
skeletal parts are greatly reduced and the fins come to consist 
mainly of the fin-rays, which are ossified and frequently become 
flattened at their distal ends. 

The tin-rays of the ventral part of the caudal fin are carried 



106 THE VERTEBRATE SKELETON. 

by the haemal arches ; those of the dorsal and anal fins and 
of the dorsal part of the caudal fin generally by interspinous 
bones, which in adult Teleosteans alternate with the neural 
and haemal spines. In Dipnoi these interspinous bones arti- 
culate with the neural and haemal spines. In many Siluroids 
the anterior rays of the dorsal and pectoral fins are developed 
into large spines which often articulate with the endoskeleton, or 
are sometimes fused with the dermal armour plates. Similar 
spines may occur in Ganoids in front of both the dorsal and 
anal fins. Polypierus has a small spine or fulcrum in front of 
each segment of the dorsal fin. Such spines are often found 
fossilised, and are known as ichthyodorulites. 

Similar spines are found in many Elasmobranchs, but they 
are simply inserted in the fiesh, not articulated to the endo- 
skeleton. They also differ from the spines of Teleosteans 
and Ganoids in the fact that they are covered with enamel, 
and often have their edges serrated like teeth. In the extinct 
Acanthodii they generally occur in front of all the fins, paired 
and unpaired. 

In Trygon, the Sting-ray, the tail bears a serrated spine 
which is used for purposes of offence and defence. Many 
ichthyodorulites may have been spines of this nature fixed to 
the tail, rather than spines situated in front of the fins. The 
spines, which are always found in front of the dorsal fin in 
Holocephali, agree with those of Elasmobranchs in containing 
enamel, and with those of Teleosteans in being articulated to 
the endoskeleton. 

TEETH. 

The teeth of fish 1 are subject to a very large amount of 
variation, perhaps to more variation than are those of any 
other class of animals. Sometimes, as in adult Sturgeons, 
they are entirely absent, sometimes they are found on all the 

1 See W. G. Eidewood, Nat. Sci. vol. vni. 1896, p. 380. Full references 
are there given to the literature of the subject. 



THE SKELETON IX FISHES. THE TEETH 



107 



bones of the mouth, and also on the hyoid and branchial 
arches. The teeth are all originally developed in the mucous 
membrane of the mouth, but they afterwards generally become 




FIG. 14. DIAGRAM OF A SECTION THROUGH THE JAW OF A SHARK (Odontaspis 
americanus) showing the succession of teeth (Brit. Mas. from 
specimen and diagram). 



1. teeth in use. 

2. teeth in reserve. 6. 

3. skin. 7. 

4. cartilage of the jaw. 

5. encrusting calcification of 



cartilage, 
connective tissue, 
mucous membrane of the 

mouth. 



attached to firmer structures, especially to the jaws. In 
Elasmobranchs, however, they are generally simply imbedded 
in the tough fibrous integument of the mouth. Their attach- 
ment to the jaws may take place in three different ways. 

(1) By an elastic hinge-joint, as in the Angler (Lophius), 
and the Pike (Esox hicius). In the Angler the tooth is held 
by a fibrous band attaching its posterior end to the subjacent 
bone, in the Pike by uncalcified elastic rods in the pulp cavity. 

(2) By ankylosis, i.e. by the complete union of the cal- 
cified tooth substance with the subjacent bone. This is the 
commonest method among fish. 



108 



THE VERTEBRATE SKELETON. 



(3) By implantation in sockets. This method is not very 
common among fish. The teeth are sometimes, as in Lepi- 
dosteus, ankylosed to the base of the socket. In this genus 
there is along each ramus of the mandible a median row of 
large teeth placed in perfect sockets, and two irregular lateral 
rows of small teeth ankylosed to the jaw. 

Dentine, enamel and cement are all represented in the teeth 
of fishes, but the enamel is generally very thin, and cement is 
but rarely developed. Dentine forms the main bulk of the 
teeth; it is sometimes of the normal type, but generally differs 
from that in higher vertebrates in being vascular, and is 
known as vasodentine. A third type occurs, known as osteo- 
dentine ; it is traversed by canals occupied by marrow, and is 
closely allied to bone. 




FIG. 15. PART OF THE LOWER JAW OF A SHARK (Galeus) 
(from OWEN after ANDRE). 



teeth in use. 

reserve teeth folded back. 

part of the caudal spine of 



a Sting-ray (Tnjgon) which has 
pierced the jaw and affected the 
growth of the teeth. 



The teeth are generally continually renewed throughout life, 
but sometimes one set persists. 

The teeth of Selachii are fundamentally identical with 



THE SKELETON IX FISHES. THE TEETH. 109 

placoid scales. They are developed from a layer of dental germs 
which occurs all over the surface of the skin, except in the 
region of the lips. At this point the layer of tooth-producing 
germs extends back into the mouth, being projected by a fold 
of the mucous membrane (fig. 14, 7). Here new teeth are 
successively formed, and as they grow each is gradually 
brought into a position to take the place of its predecessor 
by the shifting outwards of the gum over the jaw. Owing to 
this arrangement sharks have practically an unlimited supply 
of teeth (figs. 14 and 15). 

Two principal types of teeth are found in ELASMOBRAXCHS. 
In Sharks and Dogfish, on the one hand, the teeth are very 
numerous, simple, and sharp-pointed, and are with or without 
serrations and lateral cusps. Many Rays and fossil Elasmo- 
branchs, on the other hand, have broad flattened teeth adapted 
for crushing shells. Intermediate conditions occur between 
these two extremes. Thus in Cestracion and many extinct 
sharks, such as Acrodus, while the median teeth are sharp, 
the lateral teeth are more or less flattened and adapted for 
crushing. In various species belonging to the genus Baia the 
teeth of the male are sharp, while those of the female are blunt. 
A very specialised dentition is met with in the Eagle-ravs 
(Myliobatidae), in which the jaws are armed with flattened 
angular tooth-plates, arranged in seven rows, forming a com- 
pact pavement ; the plates of the middle row are very wide 
and rectangular, those of the other rows are much smaller and 
hexagonal. Lastly, in Cochliodus the individual crushing 
teeth are fused, forming two pairs of spirally-coiled dental 
plates on each side of each jaw. Pristi*, the Saw-fish, has a 
long flat cartilaginous snout, bearing a double row of persist- 
ently-growing teeth planted in sockets along its sides. Each 
tooth consists of a number of parallel dentinal columns, united 
at the base, but elsewhere distinct. 

In the HOLOCEPHALI Chimaera, Hariotta and Callorhyn- 
chus only three pairs of teeth or dental plates occur, two 



110 THE VERTEBRATE SKELETON. 

pairs in the upper jaw, one in the lower. These structures 
persist throughout life and grow continuously. The upper 
tooth structures are attached respectively to the ethmoid or 
vomerine region of the skull, and to the palato-pterygoids. The 
vomerine teeth are small, while those attached to the mandible 
and the palato-pterygoid region are large and bear several 
roughened ridges adapted for grinding food. The teeth of 
the two opposite sides of the jaw meet in a median symphysis. 
The teeth of Chimaera are more adapted for cutting, those of 
Callorhynchus for crushing. Many extinct forms are known, 
some of whose teeth are intermediate in structure between 
those of Chimaera and Callorhynchus. 

The teeth of GANOIDS are also extremely variable. Among 
living forms, the Holostei are more richly provided with teeth 
than are any other fishes, as they may occur on the pre- 
maxillae, maxillae, palatines, pterygoids, parasphenoid, vorners, 
dentaries, and splenials. Among the Chondrostei, on the other 
hand, the adult Acipenseridae are toothless ; small teeth how- 
ever occur in the larval sturgeon, and in Polyodon many 
small teeth are found attached merely to the mucous membrane 
of the jaws. Many fossil Ganoids have numerous flattened or 
knob-like teeth, borne on the maxillae, palatines, vomers and 
dentaries. Others have a distinctly 'heterodont dentition. 
Thus in Lepidotus the preuiaxillae bear chisel-like teeth, while 
knob-like teeth occur on the maxillae, palatines and vomers. 
In Rhizodus all the teeth are pointed, but while the majority 
are small a few very large ones are interspersed. 

In TELEOSTEANS, too, the teeth are eminently variable both 
in form and mode of arrangement. The} r may be simple and 
isolated, or compound, and may be borne on almost any of the 
bones bounding the mouth cavity, and also as in the Pike, on 
the hyoid and branchial arches. The splenial however never 
bears teeth and the pterygoid and parasphenoid only rarely, 
thus differing from the arrangement in the Holostei. 

The isolated teeth are generally conical in form and are 



THE SKELETON IX FISHES. THE TEETH. Ill 

ankylosed to the bone that bears them. Such teeth are, 
with a few exceptions such as Balistes, not imbedded in 
sockets nor replaced vertically. 

In some fish beak-like structures occur, formed partly of 
teeth, partly of the underlying jaw bones. These beaks are of 
two kinds : (1) In Scarus, the parrot fish, the premaxillae and 
dentaries bear numerous small, separately developed teeth, 
which are closely packed together and attached by their 
proximal ends to the bone, while their distal ends form a 
mosaic. Xot only the teeth but the jaws which bear them 
are gradually worn away at the margins, while both grow 
continuously along their attached edge. (2) In Gymnodonts, 
e.g. Diodon, the beaks are formed by the coalescence of broad 
calcified horizontal plates, which when young are free and 
separated from one another by a considerable intervaL 

In some Teleosteans the differentiation of the teeth into 
biting teeth and crushing teeth is as complete as in Lepi- 
dvsteus. Thus in the "Wrasse (Labrus), the jaws bear conical 
slightly recurved teeth arranged in one or two rows, with some 
of the anterior ones much larger than the rest. The bones of 
the palate are toothless, while both upper and lower pharyngeal 
bones are paved with knob-like crushing teeth : such pharvn- 
geal teeth occur also in the Carp but are attached only to the 
lower pharyngeal bone, the jaw bones proper being toothless. 

In DIPNOI the arrangement of the teeth is very similar to 
that in Holocephali. The mandible bears a single pair of 
grinding teeth attached to the splenials, and a corresponding 
pair occur on the palato-pterygoids. In front of these there 
are a pair of small conical vomerine teeth loosely attached to the 
ethmoid cartilage. The palato-pterygoid teeth of Ceratodus 
are roughly semicircular in shape with a smooth convex inner 
border, and an outer border bearing a number of strongly 
marked ridges. The teeth of the extinct Dipteridae resemble 
those of Ceratodus but are more complicated. 



112 THE VERTEBRATE SKELETON. 

ENDOSKELETON. 

SPINAL COLUMN l . 

The spinal column of fishes is divisible into only two 
regions, a caudal region in which the haemal arches or ribs 
meet one another ventrally, and a precaudal region in which 
they do not meet. 

The various modifications of the spinal column in fishes 
can be best understood by comparing them with the arrange- 
ment in the simplest type known, namely Amphioxus. In 
Amphioxus the notochord is immediately surrounded by a 
structureless cuticular layer, the chordal sheath. Outside this 
is the skeletogenous layer, which in addition to surrounding 
the notochord and chordal sheath embraces the nerve cord 
dorsally, and laterally sends out septa forming the myomeres. 

The CARTILAGINOUS GANOIDS" Acipenser, Polyodon and 
Scaphirhynchus are the simplest fishes as regards their spinal 
column. The notochord remains permanently unconstricted 
and is enclosed in a chordal sheath, external to which is the 
skeletogenous layer. In this layer the development of carti- 
laginous elements has taken place. In connection with each 
neuromere, or segment as determined by the points of exit of 
the spinal nerves, there are developed two pairs of ventral 
cartilages, the ventral arches (basiventralia) and intercalary 
pieces (interventralia) ; and at least two pairs of dorsal pieces, 
the neural arches (basidorsalia) and intercalary pieces (inter- 
dorsalia). The lateral parts of the skeletogenous layer do not 
become converted into cartilage, so there are no traces of 
vertebral centra. The ventral or haemal arches meet one 
another ventrally and send out processes to protect the ven- 
tral vessels. The neural arches do not meet, but are united 
by a longitudinal elastic band. 

In Cartilaginous ganoids the only indications of metameric 

1 See H. Gadow and E. C. Abbott, Phil. Trans, vol. 186 (1895) B. 
pp. 163221. 

2 C. Hasse, Zeitschr. wiss. Zool. LVII. 1893, p. 76. 



THE SKELETON* IN FISHES. VERTEBRAL COLUMN*. 113 

segmentation are found in the neural and haemal arches. The 
case is somewhat similar with the Holocephali and Dipnoi. 

In the HOLOCEPHALI the notochord grows persistently 
throughout life, and is of uniform diameter throughout the 
whole body except in the cervical region and in the gradually 
tapering tail. The chordal sheath is very thick and includes a 
well-marked zone of calcification which separates an outer zone of 
hyaline cartilage from an inner zone. There are also a number 
of cartilaginous pieces derived from the skeletogenous layer 
which are arranged in two series, a dorsal series forming the 
neural arches and a ventral series forming the haemal arches. 
These do not, except in the cervical region, meet one another 
laterally round the notochord and form centra. To each 
neuromere there occur a pair of basidorsals, a pair of inter- 
dorsals, and one or two supradorsals. In the tail the arrange- 
ment is irregular. 

In the DIPNOI as in the Holocephali the notochord grows 
persistently and uniformly, and the chordal sheath is thick 
and cartilaginous though there are no metamerically arranged 
centra. The neural and haemal arches and spines are cartila- 
ginous and interbasalia (intercalary pieces) are present. The 
basidorsalia and basiventralia do not in Ceratodus meet 
round the notochord and enclose it except in the anterior part 
of the cervical and posterior part of the caudal region. 

In ELASMOBRAXCHII the chordal sheath is weak and the 
skeletogenous layer strong. Biconcave cartilaginous vertebrae 
are developed, and as is the case in most fishes, constrict the 
notochord vertdbraHy. 

Two distinct types of vertebral column can be distinguished 
in Elasmobranchs ' : 

1. In many extinct forms and in the living Notidanidae, 

1 C. Hasse, Das natiirliche System der Elasmobranchier auf Grundlage 
des Banes and der Entwickelung ihrer WirbeUaule, Jena, 1879 and 1885, 
and "Die fossilen Wirbel. Morph. Stadien i. IT.," Horphol. Jahrb. Bd. u. 
in. and iv. 1876 78. 

R. 8 



114 THE VERTEBRATE SKELETON. 

Ce&tracion, and Squatina, the dorsal and ventral arches do not 
meet one another laterally round the centrum, and conse- 
quently readily come away from it. 

2. In most living Elasmobranchs the arches meet laterally 
round the centrum. 

The vertebrae are never ossified but endochondral calcifica- 
tion nearly always takes place, though it very rarely reaches 
the outer surface of the vertebrae. Elasmobranchs are some- 
times subdivided into three groups according to the method 
in which this calcification takes place : 

1. Cyclospondyli (Scymnus, Acanthias), in which the 
calcified matter is deposited as one ring in each vertebra. 

2. Tectospondyli (Squatina, Raia, Trygon), in which 
there are several concentric rings of calcification. 

3. Asterospondyli (Notidanidae, Scyllium, Cestracion), 
in which the calcified material instead of forming one simple 
ring, extends out in a more or less star-shaped manner. 

In Heptanchus the length of the vertebral centra in the 
middle of the trunk is double that in the anterior and posterior 
portions, and as the length of the arches does not vary, the 
long centra carry more of them than do the short centra. 

In many Rays the skull articulates with the vertebral 
column by distinct occipital condyles. 

In BONY GANOIDS the skeletogenous layer becomes calcified 
ectochoiidrally in such a way that the notochord is pinched in 
at intervals, and distinct vertebrae are produced. Ossification 
of the calcified cartilage rapidly follows. In Amia the verte- 
brae are biconcave, in Lepidosteus they are opisthocoelous, cup 
and ball joints being developed between the vertebrae in a 
manner unique among fishes. The notochord entirely disap- 
pears in the adult Lepidosteus, but at one stage in larval life 
it is expanded vertebrally and constricted intervertebrally in 
the manner usual in the higher vertebrata, but unknown 
elsewhere among fishes. 




THE SKELETON IN FISHES. THE FINS. 115 

The tail of Arnia is remarkable from the fact that as a 
rule to each neuromere, as determined by the exit of the 
spinal nerves, there are two centra, a posterior one which 
bears nothing, and an anterior one which bears the neural aud 
haemal arches, these being throughout the vertebral column 
connected with the centra by cartilaginous discs. 

In most TELEOSTEAXS but not in the Plectognathi the neural 
arches are continuous with the centra, which are nearly always 
deeply biconcave. 

In some cases many of the anterior vertebrae are anky- 
losed together and to the skull. The vertebrae often articu- 
late with one another by means of obliquely placed flattened 
surfaces, the zygapophyses. The centrum in early stages of 
development is partially cartilaginous, but the neural arches 
and spines in the trunk at any rate, pass directly from the 
membranous to the osseous condition. 

Fixs. 

The most primitive fins are undoubtedly the unpaired ones, 
which probably originally arose as ridges or folds of skin 
along the mid-dorsal line of the body, and passed thence 
round the posterior end on to the ventral surface, partially 
corresponding in position and function to the keel of a ship. 

In long 'fish' which pass through the water with an 
undulating motion such simple continuous fins may be the 
only ones found, as in Hyxine. To support these median fins 
skeletal structures came to be developed ; these show two 
very distinct forms, viz. cartilaginous endoskeletal pieces, the 
radiaUa, and horny exoskeletal fibres, the fin-rays. Me- 
chanical reasons caused the fin to become concentrated at 
certain points and reduced at intervening regions. Thus a 
terminal caudal fin arose and became the chief organ of 
propulsion, and the dorsal and ventral fins became specialised 
to act as balancing organs. 

In some of the earlier Elasmobranchs, the Pleuracanthidae, 

82 



116 THE VERTEBRATE SKELETON. 

the endoskeletal cartilaginous radialia are directly con- 
tinuous with outgrowths from the dorsal and ventral arches 
of the A r ertebrae, and form the main part of the fin. In 
later types of Elasmobranchs the horny exoskeletal fin-rays 
have comparatively greater prominence. In bony fish, as has 
been already stated, the horny fibres are replaced by bony 
rays of dermal origin, and at the same time complete reduc- 
tion and disappearance of the cartilaginous radialia takes 
place. 

THE CAUDAL FIN. 

The caudal region of the spinal column in fishes is of 
special importance. It is distinctly marked off from the rest 
of the spinal column by the fact that the ventral or haemal 
arches meet one another and are commonly prolonged into 
spines, while in the trunk region they do not meet but com- 
monly diverge from one another. 

In some fish the terminal part of the caudal region of the 
spinal column retains the same direction as the rest of the 
spinal column. The blade of the caudal fin is then divided 
into two nearly equal portions, and is said to be diphycercal. 
This condition is generally regarded as the most primitive one ; 
it occurs in the Ichthyotomi, Holocephali, all living Dipnoi, 
Polypterus and some extinct Crossopterygii, and a few Selachii 
and Teleostei. It occurs also in deep-sea fish belonging to 
almost every group, and under these conditions obviously 
cannot be regarded as primitive, but must be looked on as 
a feature induced by the peculiar conditions of life. 

In the great majority of fish the terminal part of the 
caudal region of the spinal column is bent dorsalwards, and 
the part of the blade of the caudal fin which arises on the 
dorsal surface is much smaller than is that arising on the 
ventral surface. Such a fin is said to be heterocercal. 

Strictly speaking all fish whose tails are not diphycci v,il 
have heterocercal tails, but the term is commonly applied 



THE SKELETON IX FISHES. THE SKULL. 117 

to two-bladed tails in which the spinal column forms a definite 
axis running through the dorsal blade, while the ventral blade 
is enlarged and generally forms the functional part of the 
tail. Such heterocercal tails are found in nearly all Elasmo- 
branchii, together with the living cartilaginous Ganoidei, 
and many extinct forms belonging to the same order; Lepi- 
do*t?us, Amia, and the Dipteridae among Dipnoi, have tails 
which, though obviously heterocercal, are not two-bladed. 

The vast majority of the Teleostei and some extinct Ga- 
noidei have heterocercal tails of the modified type to which 
the term homocercal is applied. The hypural bones which 
support the lower half of the tail fin become much enlarged, 
and frequently unite to form a wedge-shaped bone which be- 
comes ankylosed to the last ossified vertebral centrum. The 
tin-rays then become arranged in such a way as to produce a 
secondary appearance of symmetry. Some homocercal fish 
such as the Perch have the end of the notochord protected 
by a calcified or completely ossified sheath, the urostyle, to 
which several neural and haemal arches may be attached, and 
which becomes united with the centrum of the last vertebra ; 
in others such as the Salmon the end of the notochord is pro- 
tected only by laterally placed lxny plates. 

THE SKULL. 

It is often impossible to draw a hard and fast line between 
the cranium and the vertebral column. This is the case for 
instance in Acipenser (fig. 18, 16) among Chondrostei, in Ami. a 
among Holostei, and in Ceratodus and Protopterus among 
Dipnoi. The occipital region of the skull in Amia is clearly 
formed of three cervical vertebrae whose centra have become 
absorbed into the cranium, while the neural arches and spines 
are still distinguishable. 

The simplest type of cranium is that found in ELASMO- 
BRANCHS: it consists of a simple cartilaginous box, which is 
generally immovably fixed to the vertebral column, though 



118 



THE VERTEBRATE SKELETON. 



in some forms, like Scymnus and Galeus, a joint is indicated, 
and in others, such as the Rays, one is fairly well developed. 




FIG. 16. A. SKULL OF Notidanus x (Brit. Mus.). B. SKULL OF 
Cestracion x ^ (after GEGENBAUK). In neither case are the branchial 
arches shown. 

1. rostrum. 6. Meckel's cartilage. 

2. olfactory capsule. 7. teeth. 

3. ethmo-palatine process. 8. labial cartilage. 

4. palatine portion of palato- 9. hyomandibular. 

pterygo-quadrate bar. 10. postorbital process. 

5. quadrate portion of bar. II. optic foramen. 

The cranium in Elasmobranchs is never bony, though the 
cartilage is sometimes calcified. It is drawn out laterally 
into an antorbital process in front of the eye, and a post- 



THE SKELETON IX FISHES. THE SKULL. 119 

orbital process behind it. The nasal capsules are always carti- 
laginous, and the eye, as a general rule, has a cartilaginous 
sclerotic investment The cranium is often prolonged in 
front into a rostrum which is enormously developed in Pristis 
and some Rays. The cartilaginous roof of the cranium is 
rendered incomplete by the presence of a large hole, the an- 
terior fontanelle. 

Two pairs of labial cartilages (6g. 16, B, 8) are often 
present. They lie imbedded in the cheeks outside the anterior 
region of the jaws, and are specially large in Squatina. 

X* regards the visceral arches 1 the simplest and most primi- 
tive condition of the jaws is that of the Notidanidae, in which 
the mandibular and hyoid arches are entirely separate. In 
these primitive fishes the palato-pterygo-quadrate bar articu- 
lates with the postorbital process (fig. 16, 10), while further 
forwards it is united to the cranium by the ethmo-palatine 
ligament. The hyoid arch is small and is broadly overlapped by 
the mandibular arch. The term autostylic is used to describe 
this condition of the suspensorium. From this condition we 
pass in the one direction to that of Cestracion (fig. 16, B), in 
which the whole of the palato-pterygo-quadrate bar has become 
bound to the cranium, and in the other to that of ScyUium. 
In Sctjllium (fig. 6). while the ethmo-palatine ligament is 
retained, the postorbital articulation of the palato-pterygo- 
quadrate has been given up, so that the palato-pterygo-quadrate 
comes to abut on the hyomandibular and is attached to it by 
ligaments. The pre-spiracular ligament (fig. 16, 20) running 
from the auditory capsule also assists in supporting the jaws. 

Lastly we come to the purely hyostylic condition met 
with in Rays, in which the mandibular arch is entirely sup- 
ported by the hyomandibular. In some Rays the hyoid is 
attached to the posterior face of the hyomandibular near its 
proximal end, and may even come to articulate with the 
cranium. 

1 See H. B. Pollard, Anat. Anz. x. 1894. 



120 



THE VERTEBRATE SKELETON. 



The visceral arches of Elasmobranchs may be summa- 
rised as follows : 

1. The mandibular arch, consisting of a much reduced 
dorsal portion, the pre-spiracular ligament, and a greatly de- 
veloped ventral portion from which both upper and lower 
jaws are derived. The mandible (Meckel's cartilage) is the 
original lower member of the mandibular arch, and from it 
arises an outgrowth which forms the upper jaw or palato- 
pterygo-quadrate bar. In Scymnus this bears a few branchio- 
stegal rays. 

2. The hyoid arch, which consists of the hyomandibular 
and the hyoid, and bears branchiostegal rays on its posterior 
face. 

3. The branchial arches, generally five in number, all 
of which except the last bear branchiostegal rays. In the 
Notidanidae the number of branchial arches is increased 




FIG. 17. DORSAL VIEW 
Heptanchus. 

basi-hyal. 

cerato-hyal. 

second hypo-branchial. 

first cerato-branchial. 

first epi-branchial. 

first pharyngo-branchial. 



OF THE BRANCHIAL AKCHES OF 
(From GEGENBAUR). 

7. pharyngo-branchial, common 

to the sixth and seventh 
arches. 

8. basi-branchial of second arch. 

9. basi-branchial, common to the 

sixth and seventh arches. 



THE SKELETON IX FISHES. THE SKULL. 121 

beyond the normal series, thus in Hexanchus there are six, and 
in Heptanchus seven. There are six also in Chlamydoselache 
and Protopterus. 

4. The so-called external branchial arches which are carti- 
laginous rods attached to all the visceral arches. They are 
especially large in Cestracion. 

The skull in HOLOCEPHALI is entirely cartilaginous. The 
palato-pterygo-quadrate bar is fixed to the cranium, and to 
it the mandible articulates. There is a well-marked joint 
between the skull and the spinal column. 

In living Cartilaginous GANOIDS the primitive cartilaginous 
cranium is very massive, and is greatly prolonged anteriorly, 
while posteriorly it merges into the spinal column. Although it 
is mainly cartilaginous a number of ossifications take place in 
the skull, and membrane bones are now found definitely de- 
veloped, especially in connection with the roof of the cranium. 
In Acipenser (fig. 18) the ossifications in the cartilage include 
the pro-otic, which is pierced by the foramen for the fifth nerve, 
the alisphenoid, orbitosphenoid, ectethmoid, palatine, pterygoid, 
meso-pterygoid, hyomandibular (fig. 18, 11), cerato-hyal, all the 
cerato-branchials, and the first two epi-branchials. Most of 
these structures are, however, partly cartilaginous, though 
they include an ossified area. The membrane bones too of 
Acipenser are very well developed, they include a bone occu- 
pying the position of the supra-occipital, and form a complete 
dorsal cephalic shield. Resting on the ventral surface are a 
vomer and a very large parasphenoid (fig. 18, 3). There is a 
bony operculum attached to the hyomandibular, and membrane 
bones representing respectively the maxilla and dentary are 
attached to the jaws. The suspensorium is most markedly 
hyostylic. The palato-pterygo-quadrate bar has a very curious 
shape and is quite separate from the cranium. It is connected 
to the hyomandibular by a thick symplectic ligament con- 
taining a small bone homologous with the symplectic of 
Teleosteans. 



122 



THE VERTEBRATE SKELETON. 



Polyodon differs much from Acipenser, the membrane bones 
not being so well developed though they cover the great carti- 
laginous snout. 

The skull in Polypterus (Crossopterygii) shows a great 
advance towards the condition met with in Teleostei. The 
cranium remains to a great extent unossified, and large dorsal 
and ventral fontanelles pierce its walls. It is covered by a 




FIG. 18. LATERAL VIEW OF THE SKULL or A STURGEON (Acipenser 
sturio). Nearly all the membrane bones have been removed (Brit. 
Mus.). 



1. nasal cavity. 

2. orbit. 

3. parasphenoid. 

4. vomer. 

5. pterygoid. 

6. maxilla. (The dotted line 

running from 6 passes 
into the mouth cavity.) 

7. dentary. 

8. symplectic. 



10. palatine. 

11. hyomandibular. 

12. pharyngo-branchial. 

13. epi- branchial. 

14. cerato-branchial. 

15. hypo-branchial. 

16. coalesced anterior vertebrae. 

17. inter-hyal. 

18. cerato-hyal. 

19. rib. 



great development of membrane bones, paired nasals, frontals, 
parietals, supra- and post-temporals, and dermo-supra-occipitals 
among others being present. The palato-pterygo-quadrate bar 
is fused to the cranium, and in connection with it the following 
paired membrane bones appear, palatine, ecto-, meso- and meta- 
pterygoid, and further forwards jugal, vomer, maxilla and 
premaxilla. The membrane bones developed in connection 



THE SKELETON IX FISHES. THE SKULL. 123 

with each ramus of the mandible are the dentary, angular, 
and splenial, in addition to the cartilage bone the articular. 
Several large opercular bones occur. There are also a pair of 
large jugular or gular plates, and several large opercular bones. 

In Bony Ganoids both cartilage bone and membrane 
bone is well developed. The pro-otics and exoccipitals are 
well ossified, but the supra-occipital and pterotics are not. 
Lateral ethmoids are developed, and there are ossifications in 
the sphenoidal region which vary in different forms. The 
place of the cartilaginous palato-pterygo-quadrate is taken by 
a series of bones, the quadrate behind and the palatine, ecto-, 
meso- and meta-pterygoids in front. In Lepidosteus, however, 
the palatine and pterygoid are membrane bones, as they are 
in Polypttrus and the Frog. Paired maxillae, premaxillae, 
voiners and a parasphenoid occur forming the upper jaw and 
roof of the mouth, and a series of membrane bones are found 
investing the mandible and forming the operculum. 

In Amia 1 membrane bones are as freely developed as they 
are in Teleosteans ; they include on each side a squamosal, 
four opercular bones, a lachrymal, a pre-orbital, one or two 
suborbitals, two large postorbitals and a supratemporal ; while 
investing the mandible, besides the dentary, splenial, angular, 
and supra-angular, there is an unpaired jugular. The articular 
too is double and a inento-rneckelian occurs. In Amia teeth 
are borne on the premaxillae, maxillae, vomers, palatines and 
pterygoids. 

Bony Ganoids are the lowest animals in which squamosal 
bones are found, and they do not occur in Teleosteans. 

The suspensorium in bony Ganoids, as in the Chondrostei, 
is hyostylic, and there are two ossifications in the hyoman- 
dibular cartilage, viz. the hyomandibular, and the symplectic. 

1 T. W. Bridge. "The Cranial Osteology of Amia calca," J. Anat. 
Physiol. norm. path. 1876, vol. xi. p. 605. B. Shufeldt, "The Osteology 
of Amia calva," Ann. Rep. of the Commissioner for Fish and Fisheries. 
Washington, 1885. 



124 THE VERTEBRATE SKELETON. 

The skull of TELEOSTEI is very similar to those of Lepidosteus 
and Amia. Although the bony skull is greatly developed and 
very complicated, much of the original cartilaginous cranium 
often persists. Membrane bones are specially developed on 
the roof of the skull where they include the parietal, frontal, 
and nasal bones. The same bones are developed in connection 
with the upper jaw and roof of the mouth as in bony Ganoids, 
but only two membrane bones occur in the lower jaw, viz. the 
angular and dentary. A number of large ossifications take 
place in the cartilage of the auditory capsules. In some forms 
parts of the last pair of branchial arches are broadened out 
and form the pharyngeal bones which bear teeth. The oper- 
cular bones and those of the upper and lower jaws are quite 
comparable to those of bony Ganoids. 

A full account of the Teleostean skull has been given in 
the case of the Salmon (pp. 87 96) and the Cod (pp. 96 
101). 

In DIPXOI the skull is mainly cartilaginous, but both 
cartilage- and membrane-bone occur also. Cartilage-bone is 
found in the ossified exoccipitals, while of membrane-bones 
Protopterus has among unpaired bones a fronto-parietal, a 
median ethmoid, and a parasphenoid, and among paired bones 
nasals and large supra-orbitals. The skull of Ceratodus (fig. 19) 
has an almost complete roof of membrane bones, including some 
whose homology is doubtful. The ethmo-vomerine region is 
always cartilaginous, but bears small teeth. The palato- 
pterygo-quadrate bar is ossified and firmly united to the 
cranium, and the mandible articulates directly with it (auto- 
stylic). Membrane bones are freely developed in connection 
with the mandible, dentary, splenial, and angular bones being 
all present. There are two opercular bones. 

In the extinct Dipteridae the cranium is very completely 
covered with plates of dermal bone, and the skeleton in 
general is more ossified than is the case in recent Dipnoi. 

Six pairs of branchial arches occur in Protopterus ; Cera- 



THE SKELETON IN FISHES. THE RIBS. 



125 



todus and Lepidosiren have five, like most other fish. The 
branchial arches bear gill rakers. 




FIG. 19. DORSAT. (TO THE LEFT) AND VENTRAL (TO THE RIGHT) VIEWS 
OF THE CRANIUM OF Ceratodiis miolfpis (after GATHER). 



1. cartilaginous part of the 

quadrate with which the 
mandible articulates. 

2. scleroparietal. 

3. frontal. 

4. ethmoid. 

5. nares. 

6. orbit. 



7. pre-opercular (squamosal). 

8. second rib. 

9. first rib. 

10. vomerine tooth. 

11. palato-pterygoid tooth. 

12. palato-pterygoid. 

13. parasphenoid. 

14. interopercular. 



RIBS. 

As has been already mentioned (p. 21), although ribs 
commonly appear to be the cut-off ends of the transverse pro- 
. they are really elements derived from the ventral or 
haemal arch. 

In Elasmobranchii and other cartilaginous fish they have 
the form of small cartilaginous structures imperfectly separated 



126 THE VERTEBRATE SKELETON. 

from the diverging halves of the ventral arch, and are often 
absent. 

In Teleostei and bony Ganoids they often have different at- 
tachments in different parts of the body. In the tail region they 
are not differentiated from the two halves of the ventral arch, 
which meet in the middle line, and are prolonged into a 
haemal spine. In the posterior trunk region they sometimes 
form distinct processes diverging from the two halves of the 
ventral arch ; while further forward they may shift their 
attachment so as to arise from the dorsal side of the two 
halves of the ventral arch and at some distance from their 
ends, which now diverge as ventri- lateral processes. 

APPENDICULAR SKELETON. 
PECTORAL GIRDLE. 

The simplest type of pectoral girdle is found in Elasmo- 
branchs. It is entirely cartilaginous and consists of a curved 
ventrally-placed rod, ending dorsally in two horn-like scapular 
processes which are sometimes attached to the cranium or 
vertebral column. In Rays the shoulder girdle is very large, 
and has a distinct suprascapular portion forming a broad plate 
attached to the neural spines of the vertebrae. There is often 
a cup-like glenoid cavity for the articulation of the limb ; this 
cavity is specially large in Rays and is much pierced by holes. 
In Dipnoi the cartilaginous girdle still occurs, but on it there is 
a deposit of membrane bone forming the clavicle, inf raclavicle, 
and supraclavicle. These bones, which with the exception of 
the clavicle, are unknown in higher vertebrates, are better 
developed in Ganoids, and best of all in Teleosteans. They 
are connected by the supra- temporal with the epi-otic and 
opisthotic regions of the cranium. Owing to this development 
of dermal bone, the original cartilaginous arch becomes much 
reduced, but ossifications representing the scapula and cora- 
coid occur in bony Ganoids and Teleosteans. 



THE SKELETON IX FISHES. PAIRED FINS. 127 

PELVIC GIRDLE. 

In Elasruobranchs the pelvic girdle consists of a short 
ventral rod of cartilage representing the ischium and pubis, 
which does not send up dorsal iliac processes. In Chimaera 
the pelvic girdle has a flattened pointed iliac portion, and 
ventrally an unpaired movable cartilaginous plate which 
bears hooks and is supposed to be copulatory in function. 
Claspers of the usual type are present as well. The Dipnoi 
have a primitive kind of pelvis in the form of a cartilaginous 
plate lying in the ni id ventral line and drawn out into three 
horns anteriorly. In Ganoids the pelvis has almost entirely 
disappeared, though small cartilaginous vestiges of it remain 
in Polypterns. In Teleosteans even these vestiges are gone, 
and in these fish and Ganoids the place of the pelvis is taken 
by the enlarged basi-pterygia (meta-pterygia) of the fins. 

PAIRED Fixs 1 . 

A- regards the origin of the limbs or paired fins of fishes 
there are two principal views. One view, that of Gegenbaur, 
considers that limbs and their girdles are derived from visceral 
arches which have migrated backwards. The other view, which 
probably now has the greater number of supporters, considers 
that the paired fins of fishes are of essentially the same nature 
as the median fins. 

According to Gegenbaur's view* the archipterygium of 

L'tratodus (fig. 20) represents the lowest type of fin : it con- 

f a central cartilaginous axis bearing a large number of 

radialia. The dorsal or pre-axial rudialia are more numerous 

than the ventral or postaxial, and at the margin of the fin 3 the 

1 A. Smith Woodward, Sat. Sci. vol. 1. 1892, p. 28. Further references 
are here given on the literature of the subject. 

- C. Gegenbaur, Ueber das Archipterygium, Jena Zeitschr. der Wirbel- 
thiere, 2 e Heft, 1873, vol. 7, and Mnrphol. Jahrb. xxn. 1894, p. 119. 

3 The fins of Ceratodus are very variable, no two being exactly alike. 
Sometimes even the main axis bifurcates. See W. A. Haswell, Linn. 
Soc. JY. S. Wales, vol. vn. 1*82. 



128 



THE VERTEBRATE SKELETON. 



O "-i 

1 1 -j J 

.S o O s 

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THE SKELETON IX FISHES. PAIRED FINS. 129 

cartilaginous endoskeletal radialia are replaced by horny exo- 
skeletal fin-rays. 

It is impossible here to give a full discussion of the rival 
views, but some of the points which support Gegenbaur's view 
may be mentioned. The fact that migration of visceral arches 
has to be assumed is no difficulty, as it is obvious that 
migration in the opposite direction has taken place in many 
Teleosteans such as the Cod, whose pelvic fins are attached 
to the throat in front of the pectorals. If migration did take 
place, the pelvic fins being older than the pectoral should be 
the more modified, and this is the case. Again, if the pectoral 
girdle is a modified branchial arch, it must at some period 
have carried a gill, and in Protopterus it does bear a vestigial 
gill. 

According to the view more prevalent at the present time, 
the paired fins have been derived from two continuous folds 
of skin and their skeletal supports running forward from the 
anal region along the sides of the body, their character being 
similar to the fold that gave rise to the median fins. In 
support of this view it may be argued that the paired and 
unpaired fins are often identical in structure, and that some 
Elasmobranch embryos do show a ridge running between the 
pectoral and pelvic fins. Then from this continuous fold two 
pairs of smaller folds may have been specialised off, and in 
each a number of cartilaginous radialia may have been de- 
veloped. The fin of Cladoselache from the Carboniferous of 
Ohio apparently illustrates this condition. It consists of 
certain basal pieces which do not project beyond the body 
wall and bear a number of unsegmented cartilaginous radialia, 
which show crowding together and are sometimes bifurcated 
distally ; they extend throughout the whole fin from the body 
wall to the margin. From this fin the archipterygium might 
be easily derived by the enlargement of one of the middle 
radialia and the segmentation and partial fusion of them all. 

Whether the archipterygium be a primitive or secondary 

R. 9 



130 THE VERTEBRATE SKELETON. 

type of fin, when it is once reached it is easy to derive all the 
other types from it. The fins of the other living Dipnoi, 
Protopterus and Lepidosiren are simply archipterygia from 
which the radialia have almost or completely disappeared, 
leaving only the segmented axes. Archipterygia too are found 
in the pectoral fins of the Ichthyotomi, but the postaxial 
radialia are much reduced. 

The ichthyopterygium, or type of fin, characteristic of 
many modern Elasmobranchs such as Scyllium, may have been 
derived from the archipterygium by the gradual reduction of 
the rays on the postaxial side of the axis and their condensation 
on the pre-axial side. The Ichthyotomi such as Xenacanthus 
show one stage in the reduction of the post-axial rays, and a 
further stage is seen in the Notidanidae and some other sharks 
like Scymnus and Acanthias, in which a few postaxial rays 
still remain. The condensation of the pre-axial rays when 
further continued leads to one of the rays getting an attach- 
ment to the girdle. Thus the fin comes to articulate with the 
girdle by two basalia or basal pieces ; a third attachment is 
formed in the same way and the three basalia are called re- 
spectively pro-, meso-, and meta-pterygia. By some authors the 
meta-pterygium and by others the meso-pterygium is regarded 
as homologous with the axis of the archipterygium. 

The pectoral fins of Elasmobranchs vary very much in 
their mode of attachment. In some of the sharks, including 
the Notidanidae and Scyllium, all three basalia articulate with 
the pectoral girdle, while in others such as Cestracion the 
meta-pterygium is excluded. In Rays the pro-pterygium and 
the meta-pterygium are long and narrow and diverge much 
from one another ; other basalia work their way in between 
the meso-pterygium and meta-pterygium, and come to arti- 
culate with the pectoral girdle. Sometimes they fuse and 
form a second meso-pterygium. The radialia are greatly 
elongated and are segmented. 

In Chimaera all three basalia are present, but the meso- 



THE SKELETON IX FISHES. PAIRED FINS. 131 

pterygium is shifted and does not articulate with the pectoral 
girdle 1 . 

In Acipenser and Polyodon the pectoral fin is built on the 
same type as in Elasmobranchs, but becomes modified from the 
fact that the pro-pterygium is replaced by dermal bone which 
forms a large marginal ray. Extra meso-pterygia are formed 
in the same way as in Rays. 

In Polypterus the pro- and meta-pterygia have ossified 
while the meso-pterygium remains chiefly cartilaginous ; the 
fin-rays are also chiefly ossified. 

In Amia, Lepidosteus, and certain Teleosteans like Salmo, 
not only the pro-pterygium but the meso-pterygium is almost 
suppressed by the marginal ray. 

In the great majority of Teleosteans a still further stage is 
reached, the endoskeletal elements, the basalia and raclialia 
are almost entirely suppressed and the fin comes to consist 
entirely of ossified fin-rays of dermal origin. 

In some Teleosteans Exocaetus, a herring, and Dacti/lo- 
pterus, a gurnard the pectoral fins are so enormously developed 
that by means of them the fish is able to fly through the air 
for considerable distances. The skeleton of these great fins is 
almost entirely composed of dermal bone. 

PELVIC FIX. 

The pelvic fin is almost always further removed from the 
archipterygial condition, and is in general more modified than is 
the pectoral. Thus in the Ichthyotomi, while the pectoral fins 
are archipterygia similar to those of Cwatodus, the pelvic fins 
consist of an axis bearing rays on the postaxial side only, and 
prolonged distally into a clasper. In Dipnoi however the 
pelvic fins are very similar to the pectoral. In Elasmobranchs 
the meso-pterygium is missing, the pro-pterygium is small or 
absent, and the fin is mainly composed of the meta-pterygium 

1 Some of these views with regard to the homologies of the parts of 
the fins are not accepted by all anatomists. 

92 



132 THE VERTEBRATE SKELETON. 

(generally called basi-pterygium) and its radialia. The males 
in Elasmobranchii and Holocephali have the distal end of the 
metapterygium prolonged into a clasper. 

In Ganoids and in Teleosteans the loss of the pelvic girdle 
causes the pelvic fin to be still further removed from the 
primitive state. There is always a large basi-pterygium which 
lies imbedded in the muscles and meets its fellow at its proximal 
end. In Cartilaginous Ganoids it has a secondary segmenta- 
tion. Its relation to its fellow is subject to much variation 
in Teleosteans, sometimes as in the Perch the two are in 
contact throughout, sometimes as in the Salmon they meet 
distally as well as proximally, but are elsewhere separated by 
a space, sometimes as in the Pike and Bony Ganoids they 
diverge widely. The radialia are articulated to the basi- 
pterygium. In Cartilaginous Ganoids and Polypterus they 
are well developed, in other Ganoids and in Teleosteans they 
are in the main replaced by dermal fin-rays. 

In some Teleosteans such as the Cod the pelvic fins have 
migrated from their usual position and come to be attached 
to the throat in front of the pectoral fins. Fish with this 
arrangement are grouped together as jugulares. 



CHAPTER IX. 
CLASS II. AMPHIBIA 1 . 

AMPHIBIA differ markedly from Pisces in the fact that 
in the more abundant and familiar forms the skin is naked, 
and that when the integument is prolonged into median fins 
they are devoid of fin-rays. The notochord may persist, but 
bony vertebral centra are always developed. These are some- 
times biconcave, sometimes procoelous, sometimes opistho- 
coelous. There is only one sacral vertebra, except in rare 
cases. The cartilaginous cranium persists to a considerable 
extent but is more or less replaced by cartilage bone, and 
overlain by membrane bone. The basi-occipital is not com- 
pletely ossified, and the skull articulates with the vertebral 
column by means of two occipital condyles formed by the 
exoccipitals. 

There is a large parasphenoid, but there are no ossifications 
in the basisphenoidal, presphenoidal, and alisphenoidal re- 
gions. In most cases the epi-otics and opisthotics are ossified 
continuously with the exoccipitals. 

The palato-pterygo-quadrate bar is firmly united to the 
cranium, so the skull is autostylic. The palatines and 
pterygoids are membrane bones. Teeth are nearly always 
borne on the vomers and commonly on the maxillae and 

1 T. H. Huxley, Amphibia (Encyclopedia Britannica). 



134 THE VERTEBRATE SKELETON. 

premaxillae. There are no sternal ribs, and the sternum is 
very intimately related to the pectoral girdle. There are no 
obturator foramina. The limbs are as in the higher verte- 
brata, divisible into upper arm, fore-arm, and manus (wrist 
and hand), and into thigh, shin, and pes (ankle and foot) 
respectively. The posterior limb is, as a rule, pentedactylate, 
but in nearly every case the pollex is vestigial or absent. 

Order 1. URODELA 1 . 

The Urodela are elongated animals with a naked skin, a 
persistent tail, and generally four short limbs. 

The vertebral centra are opisthocoelous or biconcave, and 
there are numerous precaudal vertebrae. Portions of the 
notochord commonly persist in the inter vertebral spaces. In 
the skull there is no sphenethmoid forming a ring encircling 
the anterior end of the brain, its place being in many cases 
partly taken by a pair of orbitosphenoids. There is no 
quadratojugal, and the quadrate is more or less ossified. The 
mandible has a distinct splenial, and the articular is ossified. 

There is no definite tympanic cavity. The hyoid apparatus 
is throughout life connected to the quadrate by ligament, and 
a large basilingual plate does not occur. The ribs are short 
structures with bifurcated proximal ends. In the pelvis the 
pubis remains cartilaginous, and there is a bifid cartilaginous 
epipubis. The bones of the fore-arm and shin remain distinct, 
and the manus never has more than four digits. 

Suborder (1). ICHTHYOIDEA. 

The vertebrae are amphicoelous, but the notochord re- 
mains but little constricted throughout the whole length of 
the vertebral column. Three or four branchial arches nearly 
always persist in the adult. The cartilages of the carpus 
and tarsus remain unossified. 

1 See R. Wiedersheim, Morphol. Jahrb. Bd. in. 1877, p. 459. 



AMPHIBIA. URODELA. 135 

The Ichthyoidea may be subdivided again into two 
groups : 

A. Perennibranchiata, whose chief distinguishing skeletal 
characters are that the skull is elongated, the premaxillae are 
not ankylosed, the maxillae are vestigial or absent ; there are 
sometimes no nasals, and the palatines bear teeth : 

e.g. Siren, Proteus, Menobranchus. 

B. Derotremata, whose chief distinguishing skeletal cha- 
racters are that there are large maxillae and nasals ; teeth are 
borne by both maxillae and premaxillae ; there are no pala- 
tines ; and both pectoral and pelvic limbs are always present ; 

e.g. Amphiuma, Megalobatrachus, Cryptobranchu-s. 

Suborder (2). SALAMAXDRINA. 

The vertebrae are opisthocoelous. The skull is broad, and 
teeth are borne by both premaxillae and dentaries. Nasal 
bones are present. The remains of only two branchial arches 
are found in the adult. The carpus and tarsus are more or 
less ossified. 

This suborder includes the Xewts (Molge), Salamanders 
(Salamandra), and Amblystoma. 

Order 2. LABYRIXTHODOXTIA 1 . 

These are extinct Amphibia with a greatly developed 
dermal exoskeleton, which is generally limited to the ventral 
surface. The body and tail are long and in some cases limbs 
are absent. The teeth are pointed and often have the dentine 
remarkably folded. The vertebrae are amphicoelous, and are 
generally well ossified. The skull is very solid, and has a 
greatly-developed secondary roof which hides the true cranium 

1 See A. Fritsch, Fauna der Gaskohle, Prague, 1883-85-86, also writings 
of Cope, Credner, Huxley, H. v. Meyer, Miall. 



136 THE VERTEBRATE SKELETON. 

and is very little broken up by fossae. Paired dermal supra- 
occipitals are found, and there is an interparietal foramen. 
The epi-otics and opisthotics form a pair of bones distinct from 
the exoccipitals. Four simple limbs of moderate length are 
generally present, and in some cases all four limbs are pente- 
dactylate. Among the better known genera of Labyrinthodonts 
are Mastodonsaurus, Nyrania, and Archegosaurus. 

Order 3. GYMNOPHiONA 1 . 

These animals form a group of abnormal worm-like Am- 
phibia having an exoskeleton in the form of subcutaneous 
scales arranged in rings. The vertebrae are biconcave and are 
very numerous; very few however belong to the tail. The 
skull has a complete secondary bony roof, the mandible 
bears teeth and has an enormous backward projection of the 
angular. The hyoid arch has very slender cornua and no 
distinct body, it is attached neither to the cranium nor to 
the suspensorium. The ribs are very long and there are no 
limbs or limb girdles. 

Order 4. ANURA. 

These are tailless Amphibia, which except in a few in- 
stances, are devoid of an exoskeleton. The vertebrae are as 
a rule procoelous, and are very few in number. The post- 
sacral part of the spinal column ossifies continuously, forming 
an unsegmented cylindrical rod, the urostyle. Remains of the 
notochord persist, lying vertebrally, i.e. enclosed within the 
centra of the several vertebrae, and not as in Urodela lying 
between one vertebra and the next. The skull is very short 
and wide. The mandible is almost always, if not invariably, 
toothless. 

The frontals and parietals on each side are united so as to 
form a pair of fronto-parietals, and a girdle-like sphenethmoid 
is present. 

1 See R. Wiedersheim, Anatomic der Gymnophionen, Jena, 1879. 



AMPHIBIA. ANURA. 137 

The quadrate is not generally ossified. A pre-dentary or 
mento-meckelian bone is commonly present in the mandible, 
and a single bone represents the angular and splenial. The 
branchial arches are much reduced in the adult, and the distal 
ends of the cornua unite to form a flat basilingual plate of a 
comparatively large size. 

Ribs are very little developed. Clavicles are present. 
The ilia are very greatly elongated. The anterior limb has 
four well-developed digits and a vestigial pollex, and is of 
moderate length : the radius and ulna have fused. The 
posterior limb is greatly elongated and is pentedactylate ; the 
tibia and fibula are fused, while the calcaneum and astragalus 
are greatly elongated, and it is largely owing to them that 
the length of the limb is so great. The group includes the 
Frogs and Toads, the predominant Amphibia of the present 
time. 



CHAPTER X. 
THE SKELETON OF THE NEWT (Molge cristata). 

I. EXOSKELETON. 

The skin of the Newt is quite devoid of any exoskeletal 
structures. The only exoskeletal structures that the animal 
possesses are the teeth, and these are most conveniently de- 
scribed with the endoskeleton. 

II. ENDOSKELETON. 

The endoskeleton of the Newt, though ossified to a con- 
siderable extent, is more cartilaginous than is that of the frog. 
It is divisible into an axial portion including the vertebral 
column, skull, ribs, and sternum, and an appendicular por- 
tion including the skeleton of the limbs and their girdles. 

1. THE AXIAL SKELETON. 

A. THE . VERTEBRAL COLUMN. 

This consists of about fifty vertebrae arranged in a regular 
continuous series. The first vertebra differs a good deal from 
any of the others ; the seventeenth or sacral vertebra and the 
eighteenth or first caudal also present peculiarities of their 
own. The remaining vertebrae are divided by the sacrum 
into an anterior series of trunk vertebrae which bear fairly 



THE SKELETON OF THE NEWT. VERTEBRAE. 139 

large ribs, and a posterior series of caudal vertebrae, all of 
which except the first few are ribless. 

THE TRUXK VERTEBRAE. 

Any vertebra from the second to the sixteenth may be 
taken as a type of the trunk vertebrae. 

The general form is elongated and somewhat hour-glass 
shaped, and the centra are convex in front and concave 
behind ; an opisthocoelous condition such as this is quite ex- 
ceptional in Anura. The notochord may persist interverte- 
brally 1 , but in the centre of each vertebra it becomes greatly 
constricted or altogether obliterated, and replaced by marrow. 
The superficial portion of the centrum is ossified, while the 
articular surfaces are cartilaginous. The neural arches are 
low and articulate together by means of zygapophyses borne 
on short diverging processes. The anterior zygapophyses look 
upwards, the posterior downwards. Each neural arch is drawn 
out dorsally into a very slight cartilaginous neural spine. 

On each centrum, at a little behind the middle line, there 
arise a pair of short back wardly -directed transverse pro- 
cesses ; each of which becomes divided into two slightly 
divergent portions, a dorsal portion which meets the tubercular 
process of the rib and is derived from the neural arch, and a 
ventral portion which meets the capitular process of the rib 
and is derived from the ventral or haemal arch. The division 
between these two parts of the trans verse processes can be 
traced back as far as the sacrum. 

The first vertebra as already mentioned differs much 
from all the others. It has no ribs, and presents anteriorly 
two slightly divergent concave surfaces which articulate with 
the occipital condyles of the skull. Between these surfaces 
the dorsal portion of the anterior face of the centrum is 
drawn out into a prominent odontoid process, the occur- 
rence of which renders it probable that the first vertebra of 

1 i.e. between one vertebra and the next. 



140 THE VERTEBRATE SKELETON. 

the newt is really the axis, and that the atlas with the excep- 
tion of the odontoid process has become fused with the skull. 
The sacral vertebra or sacrum, differs from the vertebrae 
immediately in front of it only in the fact that its transverse 
processes are stouter and more obviously divided into dorsal 
and ventral portions. 

THE CAUDAL VERTEBRAE. 

The caudal vertebrae are about twenty-four in number. 
The anterior ones have hour-glass shaped centra, and short 
backwardly-directed transverse processes. The middle and 
posterior ones have rather shorter centra, and are without 
transverse processes. The neural arches resemble those of the 
trunk vertebrae, but each is drawn out into a rather high 
cartilaginous neural spine abruptly truncated anteriorly. All 
the caudal vertebrae except the first have also a haemal arch, 
which is very similar to the neural arch, and is drawn out 
into a haemal spine quite similar to the neural spine. Both 
neural and haemal arches are ossified continuously with the 
centra. 

B. THE SKULL. 

The skull of the newt is divisible into three principal 
parts : 

(1) an axial part, the cranium proper, which encloses 
the brain and to which 

(2) the capsules of the auditory and olfactory sense 
organs are fused ; 

(3) the skeleton of the jaws and hyoid apparatus. 
The skull is much flattened and expanded, though not so much 
as in the frog. 

(1) THE CRANIUM PROPER. 

The cranium proper or brain case is an unsegmented 
tube which remains partly cartilaginous, and is partly, con- 
verted into cartilage bone, partly sheathed by membrane bone. 
The roof and floor of the cartilaginous cranium are, as is 



THE SKELETON OF THE NEWT. THE CRANIUM. 141 

the case also in the frog, pierced by holes or fontanelles, and 
these are so large that the main part of the roof and floor 
conies to be formed by membrane bone. 

Two pairs of large ossifications take place in the cranial 
walls. Of these the more posterior on each side represents 
the exoccipital and all three periotic bones. It bears a 
small convex patch of cartilage for articulation with the atlas, 
and with its fellow forms the boundary of the foramen magnum. 

Two foramina pierce the exoccipital just in front of the 
occipital condyle and transmit respectively the glossopharyngeal 
and pneumogastric (fig. 21, X) nerves. Lying laterally to 
these nerve openings is seen a patch of cartilage, the stapes, 
which is homologous with the stapes or proximal element of 
the colurnellar chain in the frog. Further forward in front of 
the stapes is the small opening for the exit of the facial nerve, 
and seen in a lateral view close to the orbitosphenoid, that 
for the trigeminal (fig. 21, C, 5). 

In front of these large bones the lateral parts of the 
cranial walls remain cartilaginous for a short distance, and 
then there follow two elongated bones, the orbitosphenoids 
(tig. 21, B and C, 11), pierced by the foramina for the exit 
of the optic nerves. These bones partly correspond to the 
sphenethmoid of the frog. 

The membrane bones connected with the cranium are the 
parietals, frontals and prefronto-lachrymcds on the dorsal 
surface, and the parasphenoid on the ventral surface. 

The parietals (fig. 21, A and C, 6) roof over the posterior 
part of the great dorsal fontanelle and overlap the exoccipito- 
periutics. They meet one another along a sinuous suture in 
the middle line, as do also the frontals which overlap them 
in front. The frontals and parietals both extend for a short 
distance down the sides of the cranium and meet the orbito- 
sphenoids. The prefronto-lachrynud* (fig. 21, A and C, 7) 
connect the frontals with the maxillae. 

On the ventral surface is the large parasphenoid (fig. 21, 



142 



THE VERTEBRATE SKELETON. 

22 




FlG. 21. A DORSAL, B VENTRAL, AND C LATERAL VIEWS OF THE SKULL 

OF A NEWT (Molge cristata)xty (after PARKER). 

The cartilage is dotted, the cartilage bones are marked with dots and 
dashes, the membrane bones are left white. 



1. premaxilla. 

2. anterior nares. 

3. posterior nares. 

4. nasal. 

5. frontal. 

6. parietal. 

7. prefronto-lachrymal. 

8. maxilla. 

9. vomero-palatine. 

10. parasphenoid. 

11. orbitosphenoid. 

12. pterygoid. 

13. squamosal. 



14. pro-otic region of exoccipito- 

periotic. 

15. quadrate. 

16. quadrate cartilage. 

17. exoccipital region of exoc- 

cipito-periotic. 

18. articular. 

19. articular cartilage. 

20. dentary. 

21. splenial. 

22. middle narial passage. 

II. V. VII. IX. X. foramina for 
the exit of cranial nerves. 



THE .SKELETON OF THE NEWT. SENSE CAPSULES. 143 

B, 10), which is widest behind and overlapped anteriorly 
by the vorueropalatines. 

(2) THE SEXSE CAPSULES. 

The auditory capsules become almost completely ossified 
continuously with the exoccipitals : they have been already 
described. 

The nasal capsules are large and quite unossified though 
they are overlain by membrane bone. They appear on the 
dorsal surface between the anterior nares and the nasal process 
of the premaxillae. They enclose the nasal organs, bound 
the inner side of the anterior narial opening, and are con- 
nected with one another posteriorly by a cartilaginous area. 

Developed in connection with the nasal capsules are a pair 
of rather large nasals (fig. 21, A and C, 4), which lie on the 
dorsal surface immediately in front of the frontals. Each 
forms part of the posterior boundary of one of the anterior 
nares, and the two are separated from one another in 
the middle line by the nasal process of the premaxillae 
(fig. 21, A, 1), and the opening of the middle narial passage 
(fig. 21, A and B, 22), which passes right through the skull. 

On the ventral surface of the skull and forming the greater 
part of the boundary of the posterior nares are two large 
bones, the vomero-palatines (fig. 21, B and C, 9). Each consists 
of a wide anterior portion, partly separated from its fellow in 
the middle line by the ventral opening of the middle narial 
passage, and of a long pointed posterior portion which is 
separated from its fellow by the parasphenoid, and bears a row 
of small pointed teeth formed of dentine capped with enamel. 

(3) THE JAWS. 

The upper jaw of the newt is a discontinuous structure 
divided into two parts, an anterior part which consists of 
membrane bones, the maxillae and premaxillae, and a posterior 
part which remains mainly cartilaginous. 

The premaxiJlae are united, forming a single bone, which in 



144 THE VERTEBRATE SKELETON. 

a ventral view is seen to meet the maxillae and vomero- 
palatines, and in a dorsal view to send back a nasal process 
(fig. 21, A, 1) between the nasals. 

The maxillae are large bones, each terminating in a point 
posteriorly. A single row of teeth similar to those on the 
vomero-pala tines runs along the outer margin of the maxillae 
and premaxillae. 

The posterior part of the upper jaw forms a mass of 
cartilage which extends forwards towards the maxilla as a 
long pointed process whose ventral surface and sides are over- 
lapped by a membrane bone, the pterygoid (fig. 21, 12). 

The suspensorial bones include the quadrate and squa- 
mosal. The quadrate (fig. 21, 15) which forms the true 
suspensorium is directed forwards and outwards, and is 
terminated by a patch of cartilage with which the mandible 
articulates. 

The lower jaw or mandible remains partly cartilaginous, 
while its ossifications include two membrane bones and one 
cartilage bone. The cartilage bone is the articular (fig. 21,0, 
18), it forms the posterior part of the ramus, extends forwards 
for some distance along its inner side, and is terminated 
posteriorly by a patch of cartilage which articulates with the 
quadrate. The dentary (fig. 21, C, 20) is a large bone which forms 
the anterior part and nearly all the outer half of each ramus, 
and bears teeth similar to those of the upper jaw. Attached 
to its inner face is a long slender splenial (fig. 21, C, 21). 

THE HYOID APPARATUS. 

This consists of the hyoid arch and part of the first two 
branchial arches. 

The hyoid arch (fig. 21, A, 2) consists of a pair of cornua, 
each of which is divided into two halves. The dorsal half 
forming the cerato-hyal is mainly ossified though tipped with 
cartilage, and is connected by ligament with the suspensorium. 
The ventral half (hypo-hyal) is cartilaginous, and is connected 
with the basi-branchial. 



THE SKELETON OF THE NEWT. RIBS AND STERNUM. 14:5 

The branchial arches consist of a median piece, the 
basi-branchial, which is ossified in the centre and cartila- 
ginous at either end, and of two pairs of cerato-branchials 
which are attached to the cartilaginous part (fig. 29, A, 8) 
of the basi-branchial. The first cerato-branchial is chiefly 
ossified, the second (fig. 29, A, 4) is a good deal smaller and 
is cartilaginous. Both are united dorsally to a single epi- 
branchial, which is terminated by a small cartilaginous area 
at the free end but is elsewhere well ossified. 

C. THE RIBS. 

The ribs are short imperfectly ossified structures, bifid 
at their proximal end where they articulate with the trans- 
verse processes, and tipped both proximally and distally with 
cartilage. The dorsal portion of the proximal end corresponds 
to the tuberculum of the ribs of higher animals, and the 
ventral portion to the capitulum. Some of the anterior ribs 
have a step-like notch on their dorsal surfaces. 

The second to twelfth ribs are fairly equal in size, but 
further back they decrease slightly. The ribs which connect 
the sacral vertebrae with the ilia are however large. The short 
ribs borne on the anterior caudal vertebrae are cartilaginous. 

D. THE STERNUM. 

The sternum (fig. 22, A, 6) is a rather broad plate of 
cartilage, drawn out posteriorly into a median process marked 
by a prominent ridge. On its antero-lateral margins it bears 
surfaces for articulation with the pectoral girdle. 

2. THE APPEXDICULAR SKELETON. 

A. THE PECTORAL GIRDLE. 

This is of a very simple character, and remains throughout 
life in an imperfectly ossified condition. It consists of a 
dorsal scapular portion, and a ventral coracoid portion 
partially divided into an anterior part, the precoracoid, and 
a posterior part, the coracoid. 

R. 10 



146 



THE VERTEBRATE SKELETON. 



The scapular portion is a slightly curved oblong plate; its 
proximal third the scapula (fig. 22, 1) is ossified and bounds 
part of the well-marked glenoid cavity (fig. 22, 4) ; its distal 
portion forms a large oblong cartilaginous plate, the supra- 




FlG. 22. A VENTRAL, AND B LATERAL VIEW OF THE SHOULDER GIRDLE 
AND STERNUM OF AN OLD MALE CRESTED NEWT (Mol(J6 Cristdta) X 3 

(after PARKER). 

1. scapula. 4. glenoid cavity. 

2. suprascapula. 5. precoracoid. 

3. coracoid. 6. sternum. 



THE SKELETON OF THE NEWT. ANTERIOR LIMB. 147 

The precoracoid (fig. 22, 5) forms a small forwardly- 
direeted cartilaginous plate. The coracoid (fig. 22, 3) forms 
a much larger plate, the greater part of which is unossified 
and overlaps its fellow in the middle line, the two being over- 
lapped by the sternum. Around the glenoid cavity is an area 
which is mainly ossified and is continuous with the scapula. 

B. THE ANTERIOR LIMB. 

This is divisible into three parts, the upper arm or 
brachium, the fore-arm or antibrachium, and the manus. 

The upper arm includes a single bone, the humerus. 

The humerus is a slender bone cylindrical in the middle 
and expanded at either end, the proximal part forms a 
rounded head which articulates with the glenoid cavity. 
Along the proximal part of the anterior or pre-axial surface 
runs a strong deltoid ridge. The proximal part of the post- 
axial surface also bears a small outgrowth. 

The fore-arm contains two bones, the radius and ulna, both 
of which are small and imperfectly ossified at their terminations. 

The radius (fig. 23, B, 11) or pre-axial bone is rather 
the larger of the two, and is considerably expanded at its 
proximal end. The ulna or postaxial bone is somewhat 
expanded distally, but is not drawn out proximally into an 
olecranon process. 

The manus consists of two parts, a group of small bones 
forming the carpus or wrist, and the hand. 

The carpus is in a very simple unmodified condition as 
compared with that of the Frog. It consists of a proximal 
row of two bones and a distal row of four, with one, the 
centrale, interposed between. All these bones are small and 
polygonal and are imbedded in a plate of cartilage. 

The bones of the proximal row are a smaller pre-axial bone, 
the radiale (fig. 23, B, 13), and a larger postaxial bone, which 
represents the fused ulnare and intermedium of the very 
simple carpus described on pp. 26 and 27. 

102 



148 



THE VERTEBRATE SKELETON. 



The four bones of the distal row are respectively car- 
palia 2, 3, 4 and 5. 

The hand consists of four digits, that corresponding to 
the thumb of the human hand, judging from the analogy of 
the frog probably being the one that is absent. 

Each digit consists of a somewhat elongated metacarpal 
arid of two or three phalanges. The metacarpals are contracted 
in the middle and expanded at either end. They are connected 
with the carpus by cartilage, and the articulations between the 
several phalanges, and between the metacarpals and phalanges 
are also cartilaginous. The second, third, and fifth digits 
have two phalanges apiece, the fourth, which is the longest, 





FlG. 23. A RIGHT POSTERIOR, AND B RIGHT ANTERIOR LIMB OF A NEWT 

x l (Molge cristata). 

10. humerus. 

11. radius. 

12. ulna. 

13. radiale. 

14. intermedium and ulnare fused. 

15. centrale of carpus, the pointing 

line passes across carpale 2. 

16. carpale 3. 

17. carpale 5. 



femur. 

tibia. 

fibula. 

tibiale. 

intermedium. 

fibulare. 

centrale of tarsus. 

tarsale 1. 

tarsalia 4 and 5 fused. 



I. II. III. IV. V. digits. 



THE SKELETON OF THE NEWT. PELVIC GIRDLE. 149 

has three. The second metacarpal in the specimen examined 
and figured articulates partly with carpale 2, partly with 
carpale 3. 

C. THE PELVIC GIRDLE. 

The pelvic girdle of the Newt is in a much less modified 
condition than is that of the Frog (see p. 165). It consists 
of a dorsal element, the ilium, a posterior ventral element, 
the ischium, and an anterior ventral element, the pubis, to 
which is attached an epipubis. 

The ilium is a somewhat cylindrical bone which at its 
ventral end meets the ischium, and forms part of the ace- 
tabulum. It is then directed upwards and slightly back- 
wards, and is attached to the ribs of the sacral vertebra. 

The ischia are a pair of somewhat square bones which 
meet one another in the middle line : they form part of the 
acetabulum, and are united to the ilia above. 

In front of the ischia is a narrow cartilaginous area which 
represents the pubes. Projecting forwards from it is a bifid 
cartilaginous epipubis. 

D. THE POSTERIOR LIMB. 

This is divisible into a proximal portion, the thigh, a 
middle portion, the cms or shin, and a distal portion, the 
pes. 

The thigh consists of a single bone, the femur (fig. 23, A,l), 
which has a thin shaft and expanded ends. The anterior 
part of the pre-axial border and posterior part of the postaxial 
border bear slight outgrowths. 

The cms or shin includes two short bones, the tibia and 
fibula, which are nearly equal in length. The pre-axial bone 
or tibia is a straight bone thickest at its proximal end, the 
postaxial bone or fibula (fig. 23, A, 3) is a rather stouter 
curved bone of nearly equal diameter throughout. 

The pes includes the tarsus or ankle, and the foot. 



150 THE VERTEBRATE SKELETON. 

The tarsus consists of eight small bones arranged in a 
proximal row of three, the tibiale, intermedium and fibu- 
lare, and a distal row of four tarsalia, with one bone, the 
centrale (fig. 23, A, 7), interposed between the two rows. 
In the specimen examined, the tibiale, is a small bone 
articulating with the tibia, the intermedium (fig. 23, A, 5) 
is larger and articulates with both tibia and fibula, the 
fibulare is the largest of the three and articulates with the 
fibula. 

The bones, of the distal row are tarsalia 1, 2, 3, and a 
bone representing 4 and 5 fused. In the specimen examined 
tarsale 1 is pushed away dorsally (fig. 23, A, 8), so as to lie 
between the tibiale and tarsale 2. All the tarsal bones are 
small and somewhat polygonal, and are connected with one 
another, and with the tibia and fibula on the one hand, and 
with the metatarsals on the other by a thin layer of cartilage. 

The five digits of the foot each consist of a metatarsal 
and of a certain number of phalanges. In the specimen 
examined, owing to the shifting of tarsale 1, the first meta- 
tarsal as well as the second articulates with tarsale 2, while 
the fifth metatarsal articulates partially with the bone repre- 
senting the fused tarsalia 4 and 5, partially with the fibulare. 
All the bones of the digits except the distal phalanges are 
terminated, at each end by cartilaginous epiphyses, the distal 
phalanx of each digit has a cartilaginous epiphysis only on its 
proximal end. 

The first, second, and fifth digits have two phalanges 
apiece, the third and fourth have three. 

Figure 31 B, showing a Newt's tarsus copied from Gegen- 
baur, has precisely the arrangement generally regarded as 
primitive for the higher vertebrates, except that tarsalia I 
and 5 are fused. 



CHAPTER XL 
THE SKELETON OF THE FROG 1 (Rana temp&raria). 

I. EXOSKELETOK 

The skin of the frog is smooth and quite devoid of scales 
or other exoskeletal structures. The only exoskeletal struc- 
tures met with in the frog are : 

1 . The teeth, which are most conveniently described with 
the endoskeleton. 

2. The horny covering of the ca_lcar or prehallux (see 
p. 167). 

II. EXDOSKELETOX. 

The endoskeleton of the adult frog consists partly of 
cartilage, partly of bone and each of these types of tissue 
occurs in two forms. The cartilage may be hyaline, as in 
the oruosternum and xiphisternum, or may be more or less 
calcined as in part of the suprascapula and the epiphyses 
of the limb bones. The bone may be cartilage bone, or 
membrane bone. 

The skeleton is divisible into an axial portion consisting 
of the skull, vertebral column, and sternum, and an appen- 

1 See A. Ecker, Die anatomie des Frosches, Braunschweig 1864, 
translated by G. Haslam,' Oxford, 1889, also A. M. Marshall, The Frog, 
5th edition, Manchester and London, 1894. 



152 THE VERTEBRATE SKELETON. 

dicular portion consisting of the skeleton of the limbs and 
their girdles. 

1. THE AXIAL SKELETON. 

A THE VERTEBRAL COLUMN. 

The vertebral column is a tube, formed of a series of ten 
bones which surround and protect the spinal cord. Of these 
ten bones nine are vertebrae, while the tenth is a straight rod, 
the urostyle, and is almost as long as all the vertebrae put 
together. The second to eighth vertebrae inclusive have a very 
similar structure, but the first and ninth differ from the others. 

Any one of the second to eighth vertebrae forms a bony 
ring with a somewhat thickened floor, the centrum or body, 
which articulates with the centra of the immediately preceding 
and succeeding vertebrae. The articulating surfaces are 
covered with cartilage and are procoelous, or-eenvex in front 
and -coHeave behind. The eighth vertebra is however amphi- 
coelous or biconcave. The centrum of each vertebra encloses 
an isolated vestige of the notochord. The neural arch forms 
the roof and sides of the neural canal, which is very spacious 
in the anterior vertebrae, but becomes more depressed in the 
posterior ones. The arch bears the neural spine, a low 
median ridge of variable character, and is drawn out in 
front and behind, forming the two pairs of articulating 
surfaces or zygapophyses by means of which the vertebrae 
are attached together. Of these the anterior articulating 
surfaces or prezygapophyses look upwards and slightly 
inwards, while the posterior articulating surfaces or post- 
zygapophyses look downwards and slightly outwards. The 
sides of the neural arches are drawn out into a pair of 
prominent transverse processes. Those of the second 
vertebra look somewhat forwards, those of the third look 
directly outwards or somewhat forwards, while those of 
the fourth, fifth, and sixth are directed slightly backwards, 
and those of the seventh and eighth nearly straight outwards. 



THE SKELETON OF THE FROG. SPECIAL VERTEBRAE. 153 

All the transverse processes are terminated by very small carti- 
laginous ribs. 

SPECIAL VERTEBRAE. 

The first vertebra is a ring-like structure with a much 
depressed centrum. It bears in front two oval concave sur- 
faces for articulation with the condyles of the skull, while the 
centrum is terminated behind by a prominent convex surface. 
There are as a rule no transverse processes, and the post- 
zygapophyses look downwards and outwards. Occasionally 
however transverse processes do occur. Projecting forwards 
from the centrum is a minute process better developed in the 
Newt. This resembles an odontoid process, and it has hence 
been supposed that the first vertebra is homologous with the 
axis of mammalia, and that the atlas of the frog is fused with 
the skull. 

The ninth, vertebra has very stout transverse processes 
directed backwards and somewhat upwards. They articulate 
with the pelvic girdle and hence this vertebra is regarded as 
the sacrum. The neural arch is much depressed, the centrum 
is convex in front and bears on its posterior surface two short 
rounded processes for articulation with the urostyle. 

The urostyle is a long rod-like bone forming the posterior 
unsegmented continuation of the vertebral column. It is 
probably equivalent to three vertebrae, the tenth, eleventh, 
and twelfth fused together, and to an unsegmented rod of 
cartilage which lies ventral to the notochord. The anterior end 
is expanded and bears two concave articular surfaces by means 
of which it articulates with the sacrum. A prominent ridge 
runs along the dorsal surface, but gradually diminishes when 
traced back. The anterior portion contains a canal which is 
a continuation of the neural canaL At a point not far from 
the anterior end, this canal communicates with the exterior 
by a pair of minute holes which correspond with the inter- 
vertebral foramina. 



154 THE VERTEBRATE SKELETON. 

B. THE SKULL 1 . 

The skull of the Frog consists of three principal parts : 

(1) an axial part, the cranium proper, which encloses 
the brain. To it are firmly fused 

(2) the capsules of the olfactory and auditory 
sense organs, 

(3) lastly there is the hyoid apparatus and the skele- 
ton of the jaws. 

The skull is by no means so completely ossified as is the 
vertebral column, but in addition to the cartilage bone, there 
is a great development of membrane bone in connection 
with it. 

The skull has a peculiarly flattened and expanded form 
depending on the wide lateral separation of the jaws from the 
cranium. 

(1) THE CRANIUM PROPER or Brain case. ^_ 

This is an unsegmented tube, which is widest behind. It 
remains to a considerable extent cartilaginous, but is partly 
converted into cartilage bone, partly sheathed in membrane 
bone. Its roof is imperfect, being pierced by three holes 
or fontanelles, one large anterior fontanelle (fig. 25, A, 9), 
and two smaller posterior fontanelles (fig. 25, A, 10). . 

The cartilage bones of the cranium proper are the two 
exoccipitals and the sphenethmoid. 

The exoccipitals (figs. 24, 25, and 26, 6) are a pair of 
irregular bones bounding the foramen magnum at the posterior 
end of the skull. They almost completely surround the foramen 
magnum, and bear a pair of oval convex surfaces, the occipital 
condyles, with which the first vertebra articulates. The bones 
generally called the exoccipitals of the frog include the epi-otic 

1 W. K. Parker, Phil. Trans. 161, 1871, p. 137, and W. K. Parker and 
G. T. Bettany, The Morphology of the Skull, London, 1877, p. 136. 



THE SKELETON OF THE FROG. THE SKULL. 155 



and opisthotic elements of many skulls, in addition to the 
exoccipitals. 

The patch of unossified cartilage immediately external to 
the occipital condyle is pierced by two small foramina, through 
which the ninth and tenth nerves leave the cranial cavity. 
The ninth nerve passes through the more external of these 
foramina, the tenth through the one nearer the condyle. 

A B 




FlG. 24. A DORSAL, AND B VENTRAL VIEWS OF THE CRANIUM OF A 

COMMON FROG (Eana temporaria) x 2 (after PARKER). 

In this and the next two figs, cartilage is dotted, cartilage bones are 
marked with dots and dashes, membrane bones are left white. 



1. sphenethmoid. 

.2. fronto-parietal. 

3. pterygoid. 

4. squamosal. 

6. exoccipital. 

7. parasphenoid. 

8. pro-otic. 

9. quadratojugal. 

10. maxilla. 

11. nasal. 

12. premaxilla. 

13. anterior nares. 



14. vomer. 

15. posterior nares. 

16. palatine. 

18. columella. 

19. quadrate. 

20. occipital condyle. 
II. optic foramen. 

V. VII. foramen for exit of 
trigeminal and facial nerves. 

IX. X. foramina for exit of glos- 
sopharyngeal and pneumogastric 



156 THE VERTEBRATE SKELETON. 

The foramina lie however very close together and are some- 
times confluent. The cranial walls for a considerable distance 
in front of the occipitals are unossified, but the anterior end 
of the cranial cavity is encircled by another cartilage bone, the 
sphenethmoid (figs. 24 and 25, 1) or girdle bone. This 
partly corresponds to the orbitosphenoids of the Newt's skull. 
Anteriorly it is pierced by a pair of small foramina through 
which the ophthalmic branches of the trigeminal nerve pass out. 

The anterior part of the cranial cavity is divided into two 
halves by a vertical plate, the mesethmoid. Some little 
distance behind the sphenethmoid the ventro-lateral walls of 
the cartilaginous cranium are pierced by a pair of rather pro- 
minent holes, the optic foramina (figs. 24 and 25, B, n), and 
at a similar distance further back, occupying a kind of notch 
in the pro-otic are the large trigeminal foramina, through 
which the fifth and seventh nerves leave the cranium. Between 
the trigeminal and optic foramina are the very small foramina 
for the sixth nerves (fig. 25, B, vi). 

The membrane bones of the cranium proper include the 
fronto-parietals and the parasphenoid. 

The fronto-parietals (figs. 24 and 26, A, 2) form a pair of 
long flat bones closely applied to one another in the middle line, 
the line of junction being the sagittal suture. They cover 
over the fontanelles and overlap the sphenethmoid in front. 

The parasphenoid (figs. 24 and 26, B, 7) is a bone shaped 
like a dagger with a very short handle. It lies on the ventral 
surface of the cranium, the blade being directed forwards and 
underlying the sphenethmoid ; its lateral processes underlie 
the auditory capsules. 

(2) THE SENSE CAPSULES. 

The sense capsules are cartilaginous or bony structures 
which surround the olfactory and auditory organs and are 
closely united to the cranium. 

The auditory capsules are fused with the sides of the 



THE SKELETON OF THE FROG. THE SKULL. 157 



posterior end of the cranium just in front of the exoccipitals. 
They are largely cartilaginous, but include in their anterior 




FlG. 25. A DORSAL AXD B VEXTBAL VIEW OF THE CRAXICM OF A COMMON 

FKOG (Bana temporaria) from which the membrane bones hare 
mostly been removed, x 2 (after PABKEK). 



1. sphenethmoid. 

2. palatine. 

3. pterygoid. 

4. quadrate. 

5. columella. 

6. exoccipitaL 

7. ventral cartilaginous wall of 

cranium. 



8. pro-otic. 

9. anterior fontanelle. 

10. right posterior fontanelle. 

11. quadratojugal. 

12. nasal capsule. 

n. V. VI. IX. X. foramina for 
exit of cranial nerves. 



walls a pair of irregular cartilage bones, the pro-otics (figs. 
2-1 and 25, 8). The cartilaginous area lying ventral to the 
pro-otic and external to the exoccipital is pierced by a rather 
prominent hole, the fenestra ovalis, which forms a com- 
munication between the internal ear cavity, and a space the 
tympanic cavity, which lies at the side of the head, and is 
bounded externally by the tympanic membrane. The fenestra 
ovalis is occupied by a minute cartilaginous structure, the 
stapes, and articulated partly to this and partly to a slight 
recess in the pro-otic is the columella (fig. 25, B, 5), a rod in 
part bony and in part cartilaginous, whose outer end is 



158 THE VERTEBRATE SKELETON. 

attached to the tympanic membrane. The columella and 
stapes are together homologous with the mammalian auditory 
ossicles and with the hyomandibular of Elasmobranchs. Some- 
times the term columella is used to include the whole ossicular 
chain, the columella together with the stapes. 

The olfactory or nasal capsules (fig. 25, B, 12) are fused 
with the anterior end of the cranium and differ from the 
auditory capsules in being to a great extent unossified. There 
are however two pairs of membrane bones developed in con- 
nection with them, the vomers and the nasals. They are drawn 
out into three pairs of cartilaginous processes, on the dorsal 
surface into the prenasal and alinasal processes which bound 
the external nares, and on the ventral surface towards the 
middle line into the forwardly-projecting rhinal processes. 

The nasals (figs. 24 and 26, 11) form a pair of triangular 
bones lying dorso-laterally in front of the fronto-parietals. 
Their bases are turned towards one another and their apices 
are directed outwards and backwards. They correspond in 
position with the prefrontals of the reptilian skull as well as 
with the nasals. 

The vomers are a pair of irregular bones lying on the 
ventral surface of the olfactory capsules. Each bears on 
its inner and posterior angle a group of minute pointed teeth, 
while its outer border is drawn out into three or four small 
slightly diverging processes, the two posterior of which form 
the inner boundary of the posterior nares (fig. 24, B, 15). 

(3) THE JAWS. 

The upper jaw consists of a rod of cartilage connected 
with the cranium near its two ends, but widely separated from 
it in the middle. It is almost completely overlain by membrane 
bone. With its posterior end the lower jaw articulates. 

The membrane bones of the upper jaw include first the 
premaxilla, a small bone meeting its fellow in the middle 
line, and forming the extreme anterior end of the upper jaw. 
It gives off on its dorsal surface a backwardly-projecting 



THE SKELETON OF THE FROG. THE SKULL. 



159 



process. It is connected behind with the maxilla (figs. 24 and 
26, 10), a long flattened bone which forms the greater part of 



8 5 




B 



15. 

16. 
17. 
19. 
20. 
21. 
oo 



FIG. 26. A, LATERAL VIEW OF 

CRANIUM OF A COMMON FROG 

1. sphenetnrnoid. 

J. fronto-parietal. 

3. pterygoid. 

4. squamosal. 

5. tympanic membrane. 

6. esoccipital. 

7. parasphenoid. 

8. pro-otic. 

9. quadratojugal, 

10. maxilla. 

11. nasal. 

12. premaxilla. of cranial nerves. 

13. anterior nares. 

the margin of the upper jaw, and gives off near its anterior end 
a short process which projects upwards and meets the nasal. 

Both maxilla and premaxilla are grooved ventrally, and 
bear, attached to the outer more prominent margin of the groove, 
a row of minute conical teeth. These teeth are pleurodont, 
that is, are ankylosed by their bases and outer sides to the 
margin of the jaw. Each tooth is a hollow cone, the basal 



THE SKULL, B, POSTERIOR VIEW OF THE 

(Buna temporaria) x 2 (after PARKER). 

14. mento-meckelian. 
dentary. 
angulo-splenial. 
basilingual plate, 
quadrate, 
columella. 
occipital condyle. 
anterior cornu of the hyoid 

(cerato-hyal). 
foramen magnum. 
IX. X. foramina for the exit 



23. 

II. 



160 THE VERTEBRATE SKELETON. 

part of which is formed of bone, the apical part of dentine, 
capped by a very weak development of enamel. 

The posterior end of the maxilla is overlapped by a small 
bone, the quadratojugal (figs. 24 and 26, 9), whose posterior 
end forms part of the articular surface for the lower jaw. 
Just behind the quadratojugal there is a small unossified area 
which lies at the angle of the mouth, and is connected by a 
narrow bar of cartilage with the cranium ; this forms the 
quadrate (figs. 24 and 26, 19). A backwardly-directed out- 
growth from the cartilaginous bar more or less completely 
surrounds the tympanic membrane, forming the tympanic 
ring. When followed back the maxilla and quadratojugal 
diverge further and further from the cranium, till the angle 
of the mouth comes to be separated from the foramen magnum 
by a space nearly double the width of the cranium. This space 
is bridged over to a considerable extent by two triradiate bones, 
the pterygoid and squamosal. 

The pterygoid (figs. 24 and 26, 3) is a large bone, whose 
anterior limb runs forwards meeting the maxilla and palatine; 
while its inner limb meets the auditory capsule and para- 
sphenoid, arid its outer limb runs backwards and outwards 
to the angle of the mouth. The palatine is a small transversely- 
placed bone, which connects the pterygoid with the anterior 
part of the sphenethmoid. The squamosal (figs. 24 and 26, 4) 
is a T-shaped bone whose anterior arm is pointed and passes 
forwards to meet the pterygoid. The posterior upper arm is 
closely applied to the pro-otic, while the posterior lower arm 
meets the pterygoid and quadratojugal at the angle of the jaw, 
and surrounds the narrow cartilaginous bar of the quadrate 
which goes to join the cranium. The squamosal is probably 
homologous with the squamosal together with the pre-opercular 
of Bony Ganoids. 

The quadrate and squamosal form the suspensorium by 
which the lower jaw is connected with the cranium. 

The lower jaw or mandible consists of a pair of carti- 
laginous rods (Meckel's cartilages) in connection with each 



THE SKELETON OF THE FROG. THE HYOID. 161 

of which there are developed two membrane bones and one 
cartilage bone. The cartilage bone is the mento-meckelian 
(fig. 26, A, 14), a very small ossification at the^xtreme anterior 
end. The membrane bones are the angulo-gplenial and the 
dentary. The angulo-splenial is a strong flat bone which forms 
the inner and lower part of the mandible for the greater 
part of its length. Its dorsal surface is produced into a slight 
coronoid process. The dentary (fig. 26, A, 15) is a flat 
plate which covers the outer surface of the anterior half of the 
mandible, as far forwards as the mento-meckelian. The lower 
jaw is devoid of teeth. The part of Meckel's cartilage which 
in most vertebrates ossifies, forming the articular bone, remains 
unossified in the Frog. 

THE HYOID APPARATUS. 

The hyoid. of the adult Frog is formed of the modified 
hyoid and branchial arches of the tadpole. It consists of a 
broad thin plate of cartilage, the basilingual plate (fig. 29, 
B, 1), drawn out into two pairs of long processes, the cornua. 
The basilingual plate is broader in front than behind, and is 
formed from the fused ventral ends of the hyoid and branchial 
arches of the tadpole. 

The anterior cornua (tig. 29, B, 2) form a pair of long 
slender cartilaginous rods which project from the body of the 
hyoid at first forwards, then backwards, and finally upwards 
and somewhat forwards again, to be united to the auditory 
capsules just below the fenestrae ovales. They are formed 
from the dorsal portion of the hyoid arch of the tadpole and 
are homologous with the cerato-hyals of the Dogfish. 

The posterior cornua form a pair of straight bony rods 
diverging outwards from the posterior end of the basilingual 
plate. They are formed from the fourth branchial arches of 
the tadpole, and differ from the rest of the hyoid apparatus 
in being well ossified. 

R. * 11 



162 THE VERTEBRATE SKELETON. 

The columellar chain, which has been already described 
(p. 157), should be mentioned with the hyoid as it is homo- 
logous to the hyomandibular of fishes. 

The sternum of the Frog, though regarded as part of the 
axial skeleton, is so intimately connected with the pectoral 
girdle, that it will be described with the appendicular 
skeleton. 

2. THE APPENDICULAR SKELETON. 

This consists of the skeleton of the two pairs of limbs and 
their respective girdles. It is at first entirely cartilaginous 
but the cartilage becomes later on mainly replaced by bone. 
The only bone developed in connection with the appendi- 
cular skeleton, which has no cartilaginous predecessor, is the 
clavicle,. 

A. THE PECTORAL GIRDLE. 

This consists originally of two half rings of cartilage en- 
circling the sides of the body a short way behind the head. 
These two halves meet one another in the ventral middle line, 
and separate the anterior elements of the sternum from the 
posterior ones. 

Each half-ring bears on the middle of its outer and pos- 
terior surface a prominent cup, the glenoid cavity, with 
which the proximal arm-bone articulates. This cup divides 
the half-arch into a dorsal scapular and a ventral coracoid 
portion. 

The scapular portion consists of two parts, the supra- 
scapula and the scapula. 

The suprascapula (fig. 30, A, 2) is a wide, thin plate 
attached by its ventral and narrowest border to the scapula. 
Its proximal and anterior half is imperfectly ossified, its whole 
border or sometimes only its dorsal and posterior borders consist 
of unaltered hyaline cartilage, while the rest of it is composed 
of calcified cartilage. The scapula (fig. 30, A, 3) is a fairly 



THE SKELETON OF THE FROG. THE STERNUM. 163 

stout rod of bone constricted in the middle, and forming the 
dorsal half of the glenoid cavity. 

The coracoid portion consists of three parts, the cora- 
coid, precoracoid and clavicle. 

The largest and most posterior of these is the coracoid 
(fig. 30, A, 4) which like the scapula, is contracted in the 
middle and expanded at the ends, especially at the ventral 
end. It forms a large part of the glenoid cavity. The 
ventral ends of the coracoids which meet one another in the 
middle line are unossified, and form narrow strips of calcified 
cartilage, the epicoracoids (fig. 30, A, 5) ; these are often 
regarded as sternal elements. 

The precoracoid forms a narrow strip of cartilage lying 
in front of the coracoid, from which it is separated by the 
wide coracoid foramen (fig. 30, A, 9). The dorsal end is 
continuous with an area of unossified cartilage which separates 
the coracoid and scapula and forms part of the glenoid cavity. 

The clavicle is a narrow membrane bone closely attached 
to the anterior surface of the precoracoid, its dorsal end is ex- 
panded. 

THE STERXUM. 

The sternum consists of four parts arranged in two groups: 
two parts to each group. The anterior members are the epi- 
sternum and omosternum. 

The episternum (fig. 30, A, 10) is a thin almost circular 
plate of cartilage much of which remains hyaline. 

The omosternum (fig. 30, A, 11) is a slender bony rod 
widest at its posterior end ; it connects the episternum with 
the ventral ends of the precoracoids. 

The sternum proper is a short rod of cartilage sheathed 
in bone ; it is contracted in the middle and expanded at each 
end. It bears attached to its posterior end a broad some- 
what bilobed plate of partially calcified cartilage, the xiphi- 
sternum (fig. 30, A, 13). 

112 



164 THE VERTEBRATE SKELETON. 

B. THE ANTERIOR LIMB. 

This is divisible into three parts, the upper arm or 
brachium, the fore-arm or antibrachium, and the manus. 

All the larger bones have their ends formed by prominent 
epiphyses which do not unite with the shaft till late in life. 
Their articulating surfaces are covered by hyaline cartilage. 

In the upper arm there is a single bone, the humerus. 

This has a more or less cylindrical shaft and articulates by 
a prominent rounded head with the glenoid cavity. The 
distal end shows a large rounded swelling on either side of 
which is a condylar ridge, the inner or postaxial one being 
the larger. A prominent deltoid ridge runs along the 
proximal half of the anterior surface, and in the male frog a 
second equally prominent ridge runs along the distal half of 
the posterior surface. 

The fore-arm consists of two bones, the radius and ulna, 
united together and forming the radio-ulna. The two bones 
are quite fused at their proximal ends where they form a 
deep cup which articulates with the distal end of the humerus, 
and is drawn out into a rather prominent backwardly-pro- 
jecting olecranon process, which ossifies from a centre 
distinct from that of the shaft. The distal end is distinctly 
divided by a groove into an anterior radial and a posterior 
ulnar portion. 

The manus consists of two parts, the wrist or carpus 
and the hand. 

The carpus' consists of six small bones arranged in two 
rows. The three bones of the proximal row are the ulnare, 
radiale and centrale. The ulnare and radiale are about 
equal in size and articulate regularly with the radio-ulna. The 
centrale is pushed out of its normal position and lies partly on 
the pre-axial side, partly in front of the radiale. Of the three 
bones of the distal row the two pre-axial ones, carpalia 1 and 
2, are small ; carpale 2 articulates with the second metacarpal, 
1 See G. B. Howes and W. Ridewood, P. Z. S., 1888, p. 141. 



THE SKELETON OF THE FROG. PELVIC GIRDLE. 165 

carpale 1 with both the first and second. The third bone is 
large and articulates with the third, fourth and fifth meta- 
carpals, it represents carpalia 3 5, with probably in addition 
the representative of a second centrale. 

The hand consists of four complete- digits, and a vestigial 
pollex reduced to a short metacarpal. 

Each of the four complete digits consists of a metacarpal 
and a variable number of phalanges. The first digit, as just 
mentioned, has no phalanges, the second and third have two, 
and the fourth and fifth have three. 

C. THE PELVIC GIRDLE. 

The pelvic girdle of the Frog is much modified from the 
simple or general type found in the Xewt (p. 149). 

It is a Y-shaped structure consisting of two halves which 
are fused together in the middle line posteriorly, while in 
front they are attached to the ends of the transverse pro- 
cesses of the sacral vertebra. Each half bears at its posterior 
end a deep cup, the acetabulum, with which the head of the 
femur articulates. 

Each half of the pelvis ossifies from two centres. The 
anterior and upper half of the acetabulum, and the long 
laterally compressed bar extending forwards to meet the sacral 
vertebra ossify from a single centre and are generally called 
the ilium ; it is probable however that they represent both 
the ilium and pubis of mammals 1 . The posterior part of 
this bone meets its fellow in a median symphysis. 

The posterior third of the acetabulum is formed by a small 
bone, the ischium, which likewise meets its fellow in a 
median symphysis. 

The ventral portion of the pelvic girdJe never ossifies, even 
in old animals being formed only of calcified cartilage. This 
is generally regarded as the pubis, but it perhaps corresponds 
to the acetabular bone of mammals. 

1 See bottom of p. 187. 



166 THE VERTEBRATE SKELETON. 

D. THE POSTERIOR LIMB. 

This corresponds closely to the anterior limb and, like it, 
is divisible into three parts, the thigh, the shin or eras and 
the pes. 

As was the case with the anterior limb, all the long bones 
have their ends formed by prominent epiphyses which do not 
unite with the shaft till late in life. 

In the thigh there is only a single bone, the femur. 

The femur is a moderately long, slender bone with a well- 
ossified hollow shaft slightly curved in a sigmoid manner. 
Both ends are expanded, the proximal end is hemispherical 
and articulates with the acetabulum, the distal end is larger 
and more laterally expanded. 

The shin likewise includes a single bone, the tibio-fibula, 
but this, as can be readily seen by the grooves at the proximal 
and distal ends of the shaft, is formed by the fusion of two 
distinct bones, the tibia and fibula. The tibio-fibula is longer 
and straighter than the femur. 

The pes consists of two parts, the ankle or tarsus and the 
foot. 

The tarsus consists of two rows of structures, very dif- 
ferent in size. The proximal row consists of two long bones, 
the tibiale and fibulare, which are united by common epi- 
physes at the two ends, while in the middle they are widely 
separated. The tibiale lies on the tibial or pre-axial side, 
and the fibulare which is the larger of the two bones on 
the fibular or postaxial side. The distal row of tarsals 
consists of three very small pieces of calcified cartilage. The 
postaxial of these is the largest, it articulates with the second 
and third metatarsals and is probably homologous with tarsalia 
2 and 3 fused. The middle one is very small, it articulates 
with the first metatarsal and is probably tarsale 1. The pre- 
axial one articulates with the metatarsal of the calcar, a 
structure to be described immediately, and has been regarded 
as a centrale. 



THE SKELETON OF THE FROG. THE FOOT. 167 

The foot includes five complete digits and a supplemental 
toe as well. Each of the five digits consists of a long meta- 
tarsal with epiphyses at both ends, and of a variable number 
of phalanges. The first digit or hallux and the second have 
two phalanges, the third three, the fourth, which is the largest, 
four, and the fifth, three. The distal phalanges have epi- 
physes only at their proximal ends, the others at both ends. 

On the pre-axial side of the hallux is the supplemental 
digit, the prehallux or calcar. It consists of a short meta- 
tarsal and one or two phalanges, and is terminated distally by 
a horny covering of epidermal origin. 



CHAPTER XII. 

GENERAL ACCOUNT OF THE SKELETON IN 
AMPHIBIA. 

EXOSKELETON. 

The exoskeleton, at any rate in most living forms, is very 
slightly developed in Amphibia. The only representatives 
of the epidermal exoskeleton are (1) the minute horny beaks 
found coating the premaxillae and dentaries in Siren and the 
tadpoles of most Anura, (2) the nails borne by the first three 
digits of the pes in Xenop^is and by the Japanese Salamander 
Onychodaclylus, (3) the horny covering of the calcar or pre- 
hallux of frogs. The Urodela and nearly all the Anura, which 
form the vast majority of living Amphibia, have naked skins. 
A few Anura belonging to the genera Ceratophrys and Brachy- 
cephalus have bony dermal plates developed in the skin of the 
back, and these plates become united with some of the under- 
lying vertebrae. 

In the Gymnophiona the integument bears small cycloid 
scales arranged in rings which are equal in number to the 
vertebrae. These scales contain calcareous concretions. Scales 
also occur between the successive rings. 

In the Labyrinthodontia the dermal exoskeleton is in 
many genera greatly developed. It is generally limited to the 
ventral surface and consists principally of a buckler formed 
of three bony plates, one median and two lateral. These 



THE SKELETON IX AMPHIBIA. THE TEETH. 169 

plates protect the anterior part of the thorax, and are closely 
connected with the adjacent endoskeleton. They probably 
represent the interclavicle and clavicles. Behind this buckler 
numerous scutes are generally developed, which often cover 
the whole ventral surface, and may cover the whole body. 

TEETH'. 

In Amphibia teeth are generally present on the maxillae, 
premaxillae and vomers, and except in Anura on the dentaries : 
sometimes they occur on the palatines as in many Urodela, most 
Labyrinthodontia, and the Gymnophiona; less commonly on the 
pterygoids as in Menobranchus, Siredon, some Labyrinthodontia, 
and Pelobates cuhripes' 2 , or on the splenials as in Siren and Meno- 
branchtis, or parasphenoid as in Pelobates ctdtripes, Spelerpes 
Mil and Batrackoseps. In some Anura such as Bufo and Pipa 
the jaws are toothless. 

In Gymnophiona, Menobranchus, and Siredon^ the teeth 
are arranged in two concentric curved rows. The teeth of the 
outer row are borne on the premaxillae and maxillae if present, 
(the maxillae are absent in Menobranchw}, the teeth of the 
second row on the vomers and pterygoids in Menobranckus 
and Siredon, and on the vomers and palatines in Gymnophiona. 
In some Gymnophiona there is a double row of mandibular 
teeth. The vomerine, palatine and parasphenoid teeth of all 
forms are numerous and are not arranged in rows. 

The teeth of all living Amphibia are simple conical struc- 
tures ankylosed to the bone, and consisting of dentine, coated 
or capped with a thin layer of enamel. In the Labyrinthodontia 
teeth of more than one size are sometimes present. The dentine 
of the basal part of the larger teeth is in some genera very 
greatly folded, causing the structure to be highly complicated. 
These folds, the intervals between which are filled with cement, 

1 0. Hertwig. Ueber das Zahnsystem der Amphibien. Arch. mikr. 
Anat. supplem. Bd. xi. 1875. 

- G. A. Bonlenger, P. Z. S. 1890, p. 664. 



170 THE VERTEBRATE SKELETON. 

radiate inwards from the exterior and outwards from the large 
pulp cavity. The basal part of the teeth of Ceratophrys 
(Anura) has a similar structure. 

ENDOSKELETON. 
VERTEBRAL COLUMN. 

Four regions of the vertebral column can generally be 
recognised in Amphibia, viz. the cervical, the trunk or thoraco- 
lumbar, the sacral and the caudal regions. In the limbless 
Gymnophiona, however, only three regions, the cervical, tho- 

Jracic, and post-thoracic can be made out. The cervical region 
is limited to a single vertebra which generally differs from the 
others in having no transverse processes or indication of ribs. 
It is generally called the atlas, but it commonly bears a small 
process arising from the anterior face of the centrum which 
resembles the odontoid process of higher animals, and renders 
it probable that the first vertebra of Amphibia corresponds 
to the axis, not to the atlas. Amphibia generally have a 
single sacral vertebra. 

Three elements go to make up the vertebral column in 
Amphibia, viz. 

1. the notochord, 

2. the long vertebral centra, 

3. intervertebral cartilage which forms the joints between 
successive centra. 

The relations which these three elements bear to one 
another are subject to much variation. The successive stages 
can be well traced in the Urodela. 

1. The first stage is found in larval Urodeles in general 
and in adult Ichthyoidea, and some Salamandrina. In these 
forms the notochord persists and retains approximately the 
same diameter throughout the whole length of the vertebral 
column. Bony biconcave centra are present and constrict it 



THE SKELETON IX AMPHIBIA. VERTEBRAL COLUMN. 171 

to a certain extent vertebrally, while intervertebrally there is 
a development of cartilage. The connection between the bony 
vertebrae is effected mainly by the expanded notochord. 

2. In the next stage, as seen in Gyrinophilus porphyriti- 
cus, the growth of intervertebral cartilage has caused the 
almost complete obliteration of the notochord intervertebrally, 
and its entire disappearance vertebrally, i.e. in the centre of 
each vertebra. The intervertebral cartilage now forms the main 
connection between successive vertebrae, and sometimes cases 
are found whose condition approaches that of definite articula- 
tions. Readily recognisable remains of the notochord are still 
found at each end of the intervertebral constriction. 

3. In the third stage differentiation and absorption of the 
intervertebral cartilage has given rise to definitely articulating 
opisthocoelous vertebrae. These are found in most adult 
Salamandrina. 

The transverse processes of the earlier trunk vertebrae 
are divided into two parts, a dorsal part which meets the 
tubercular process of the rib and is derived from the neural 
arch, and a ventral part which meets the capitular process of 
the rib, and is derived from the ventral or haemal arch. In 
the caudal vertebrae and often also in the posterior trunk 
vertebrae the two processes are fused. 

Siren and Proteus, although they possess minute posterior 
limbs, have no sacral vertebrae, while Cryptobranehus lateralis 
has two. The caudal vertebrae, except the first, have haemal 
arches very similar to the neural arches. 

In Labyrinthodontia the centra of the vertebrae are gene- 
rally well ossified biconcave discs. In some forms however, like 
Euchirosaurus, the centra are imperfectly ossified, and consist 
of bony rings traversed by a wide notochordal canal. Each 
ring is formed of four pieces, a large well-ossified neural arch, 
a basal piece, and a pair of lateral pieces. Vertebrae of this 
type are called rachitomous. 



172 THE VERTEBRATE SKELETON. 

In the tail region of other forms each vertebra consists 
of an anterior centrum bearing the neural arch, and a pos- 
terior intercentrum 1 bearing chevron bones. Vertebrae of this 
type are called embolomerous. Haemal arches similar to the 
neural arches are often found as in Urodela. The transverse 
processes are sometimes well developed and are divided into 
tubercular and capitular portions. 

In Gymnophiona the vertebrae are biconcave and are very 
numerous, they sometimes number about two hundred and 
thirty. Only quite the last few are ribless and so can be 
regarded as post-thoracic vertebrae. The first vertebra has 
nothing of the nature of an odontoid process. 

In Anura the number of vertebrae is very greatly reduced, 
only nine and the urostyle being present. Of these, eight are 
presacral and one sacral. The urostyle is postsacral and 
corresponds to three or more modified vertebrae. The first 
vertebra is without transverse processes, the remaining pre- 
sacral vertebrae have the transverse processes fairly large, 
while the sacral vertebra has them very large, forming in 
some genera widely expanded plates. The urostyle is a long" 
cylindrical rod which articulates with the sacrum generally by 
two facets. Ankylosed to its anterior end are the remains 
of two neural arches. 

In Anura remains of the notochord are found in the centre 
of each vertebra, i.e. vertebrally, while in the Urodela they 
only occur intervertebrally. 

The vertebrae in Anura are, as a rule, procoelous. The 
eighth vertebra is however generally amphicoelous, while 
the ninth commonly has one convexity in front, and two 
behind. 

In some forms such as Bombinator, Pipa, Discoglossus and 
Alytes they are opisthocoelous ; in others like Pelobates they 
are variable. 

1 See p. 14. 



THE SKELETON IN AMPHIBIA. THE SKULL. 173 

THE SKULL'. 

CRAXIUM AND MAXDIBLK. 

In the Amphibian skull there are as a rule far fewer bones 
than in the skull of bony fish. The primordial cartilaginous 
cranium often persists to a great extent. Only quite a few 
ossifications take place in it ; namely in the occipital region 
the exoccipitals, further forwards the pro-otics, and at the 
boundary of the orbital and ethmoidal regions the sphen- 
ethinoid. The basi-occipital and basisphenoid are never 
ossified. As in Mammalia there are two occipital condyles 
formed by the exoccipitals. 

Large vacuities commonly occur in the cartilage of both 
floor and roof of the primordial cranium. These are roofed 
over to a greater or less extent by the development of mem- 
brane bone. Thus on the roof of the cranium there are paired 
parietals, frontals, and nasals, and on its floor are paired 
vomers, and a median unpaired parasphenoid. 

In all living forms the parietals meet and there is no 
interparietal foramen, though this exists in Labyrintho- 
donts. 

The palato-pterygo-quadrate bar is united at each end with 
the cranium, but elsewhere in most cases forms a wide arch 
standing away from it. The suspensorium is, as in Dipnoi 
and Holocephali, autostylic. The palato-pterygo-quadrate bar 
sometimes remains entirely cartilaginous, sometimes its pos- 
terior half is ossified forming the quadrate. In connection 
with it a number of membrane bones are generally developed, 
viz. the maxillae, premaxillae, palatines, pterygoids, quadrato- 
jugals, and squamosals. The pterygoids are, however, some- 
times partially formed by the ossification of cartilage. The 

1 See many papers by W. K. Parker published in the Phil. Trans, of 
the Royal Soc. 



174 THE VERTEBRATE SKELETON. 

cartilage of the lower jaw and its investing membrane bones 
generally have much the same relations as in bony fishes. 

URODELA. The skulls of the various Urodeles show an 
interesting series of modifications and differ much from one 
another, but all agree in the absence of the quadratojugals, 
in the fact that the palatines lie parallel to the axis of the 
cranium, and in the large size of the parasphenoid. 

The lower types Menobranchus, Siren, Proteus, and Am- 
phiuma have longer and narrower skulls than do the higher 
types. 

Menobranchus has a very low type of skull which remains 
throughout life in much the same condition as that of a young 
tadpole or larval salamander. The roof and floor of the 
cranium internal to the membrane bones are formed of fibrous 
tissue, not of well-developed cartilage. The epi-otic regions of 
the skull are ossified, forming a pair of large bones which lie 
external to, and distinct from, the exoccipitals. Proteus and 
the Labyrinthodonts are the only other Amphibia which have 
these elements separately ossified. The parietals send a pair 
of long processes forwards along the sides of the frontals. 
Nasals and maxillae are absent, as is likewise the case in 
Proteus. Teeth are borne on the vomers, premaxillae, ptery- 
goids, dentaries and angulo-splenials. The suspensorium is 
forwardly directed. 

The skull of Siren resembles that of Menobranchus in 
several respects, as in the forward direction of the suspen- 
sorium and in the absence of maxillae, but differs in the 
possession of nasals, in the toothless condition of the pre- 
maxillae and dentaries, and in the fusion and dentigerous con- 
dition of the vomers and palatines. 

Amphiuma has a skull which, though narrow and elongated, 
differs from those of Menobranchus, Proteus, and Siren, and 
resembles those of higher types in the following respects : 

(1) the suspensorium projects nearly at right angles to 



THE SKELETON IN AMPHIBIA. THE SKULL. 175 

the cranium instead of being directed forwards, (2) the 
maxillae are well developed, and the premaxillae are com- 
pletely ankylosed together, (3) there are no palatines. 

The skulls of Megalobatrach us, Cryptobranchus and Siredon 
resemble those of the highest Urodeles the Salamanders in their 
wide form, in having the pro-otics distinct from the exoccipitals 
which are ossified continuously with the epi-otics and opisth- 
oties. and in having no palatines, but differ in having the two 
premaxillae separate, and in the arrangement of the vomerine 
teeth which in Megalobatrachus and Cryptobranchus are placed 
along the anterior boundaries of the bones, these meeting in 
the middle line. In Siredon the vomers are separated by the 
very large parasphenoid. 

The suspensorium in Meyalobatrachus and Cryptobranchv* 
projects at right angles to the cranium ; in Siredon it projects 
somewhat downwards and forwards as in the Salamandrina. 

Modifications of the vomers, pterygoids and palatines ac- 
company the changes of the larval ichthyoid Siredon into the 
adult salamandroid AmUystoma, the vomers especially come 
to resemble to a much greater extent those of the Sala- 
mandrina. 

The ossification of the skull in the Salamandrina is carried 
further than in the Ichthyoidea, though the supra-occipital and 
basi-occipital are not ossified. The skull differs from that in 
the Ichthyoidea in the size of the part of the vomero-palatines 
which lies in front of the teeth, in the frequent union of the 
two premaxillae and in the ossification of all the periotic bones 
continuously with the exoccipital. 

The skull differs from that of Anura in the following 
respects : 

(1) the bones of the upper jaw do not form a complete 
arch standing away from the cranium, and the maxillae are 
not united to the quadrates by quadratojugals, (2) the long 
axis of the suspensorium passes obliquely downwards and 
forwards instead of downwards and backwards, (3) there is no 



176 



THE VERTEBRATE SKELETON. 



sphenethmoid encircling the anterior end of the brain, its place 
being partly taken by a pair of orbitosphenoids, (4) there is no 
definite tympanic cavity. 




FIG. 27. DORSAL VIEW OF THE SKULL OF A LABYRINTHODONT 

saurus nasutus) x (from VON ZITTEL). 

1. premaxilla. 12. postorbital. 

2. nasal. 13. interparietal foramen 

3. maxilla. 14. squamosal. 

4. anterior nares. 15. supratemporal. 

5. frontal. 16. quadratojugal. 

6. prefrontal. 17. quadrate. 

7. lachrymal. 18. epi-otic. 

8. jugal. 19. dermo-supra-occipital 

9. orbit. 20. exoccipital. 

10. parietal. 21. foramen magnum. 

11. postfrontal. 



LABYRINTHODONTIA. The skull in Labyrinthodontia is 
markable for its extreme solidity, the large number of bone 
which are present, and the extent to which the roofing over 



THE SKELETON IX AMPHIBIA. THE SKULL. 177 

the temporal and other fossae has taken place. In many 
forms the surface of the bones is as in Crocodiles, strongly 
sculptured (fig. 27, right half) with ridges and grooves which 
probably lodged sensory organs. The bones forming the 
roof of the skull are generally very uniform in size, perhaps 
the most noticeable of them being the paired dermo-supra- 
occipitals (fig. 27, 19). Paired dermo-supra-occipitals occur 
also in certain Ganoids. The Labyrinthodont skull also 
bears resemblance to that of many fish in the development 
of a pair of long pointed epi-otics (tig. 27, 18), which remain 
permanently distinct from the surrounding bones. The pa- 
rietals are small and enclose between them the interparietal 
foramen (fig. 27, 13). In some forms in which the head is 
protected with an armour of scutes, these do not roof over 
the interparietal foramen, and from this fact it has been 
inferred that the Labyrinthodonts had a functional pineal 
eye. Both supra- and infra-temporal fossae are partially or 
completely roofed over by the postorbitals and large supra- 
temporals (fig. 27, 15). 

There is generally a ring of bones in the sclerotic coat 
of the eye. The pterygoids do not meet in the middle line, 
being separated by the parasphenoid. The palatines bear 

i teeth, and in some genera (Archegosaurus) form long splints 
lying along the inner side of the maxillae and more or less 

\ surrounding the posterior nares. In others (Nyrania) they 
lie in the normal position near the middle line, one on 

i each side of the parasphenoid. The vomers bear teeth and 
sometimes meet in the middle line ; they are sometimes 
confluent with the parasphenoid. On the ventral surface 
of the cranium there are generally large palatal vacui- 
ties. 

In the mandible there is often a well-marked postglenoid 
process, and the articular is generally completely ossified. 

GYMXOPHIOXA. The skull bears a considerable resemblance 
to that of Labyrinthodonts, especially in the arrangement of 
R. 12 



178 



THE VERTEBRATE SKELETON. 
1 \ ,2 



-5 



-14 




-10 



12 



FlG. 28. A, VENTRAL VIEW OF THE CRANIUM ; B, LATERAL VIEW OF THE 

CRANIUM AND MANDIBLE OF Siplwnops annulatus (after WIEDEHSHEIM). 



1. anterior nares. 

2. naso-premaxilla. 

3. frontal. 

4. parietal. 

5. maxilla. 

6. vomer. 

7. orbit. 

8. quadrate united with the 

pterygoid in front. 



9. squamosnl. 

10. exoccipital. 

11. dentary. 

12. angular. 

13. basi-occipital and basispl 

noid fused. 

14. posterior narial opening su 

rounded by the palatine. 
X. pneumogastric foramen. 



THE SKELETON IN AMPHIBIA. THE SKULL. 179 

the bones -which bound the mouth cavity. The cranium is 
very hard, and is covered by a complete bony roof formed 
mainly of the exoccipitals, parietals, frontals, prefrontals, 
nasals and premaxillae. The nasals and premaxillae are 
sometimes ossified continuously. There is a median unpaired 
ethmoid whose dorsal end appears at the surface wedged in 
! between the frontals and parietals. The bone generally 
regarded as the squamosal 1 is very large, and it and the 
maxilla generally together surround the orbit, which, in 
Epicrium, has in it a ring of bones. The palatines form long 
tooth-bearing bones fused with the inner sides of the maxillae ; 
they nearly surround the posterior nares. 

The quadrate bears the knob, and the angular the cup 
for the articulation of the mandible, a very primitive feature. 
The mandible is also noticeable for the enormous backward 
projection of the angular. 

ANURA. In Anura the skull is very short and wide 
owing to the transverse position of the suspensorium. There 
is often a small ossification representing the quadrate. Some- 
times as in Hyla and Alytts there is a fron to-parietal 
fontanelle. 

As compared with the skull in Urodela the chief charac- 
teristics of the skull of Anura are : 

1. the presence of a sphenethmoid, 

2. the union of the frontals and parietals on each side, 

3. the occasional occurrence of small supra- and basi- 
occipitals, 

4. the backward growth of the maxilla and its connection 
with the suspensorium by means of the quadratojugal, 

5. the dagger-like shape of the parasphenoid, 

6. the occurrence of a definite tympanic cavity, 

1 Perhaps this bone includes supra-orbital and postorbital elements. 

122 



180 THE VERTEBRATE SKELETON. 

7. the frequent occurrence of a pre-dentary or mento- 
meckelian ossification in the mandible. 

The skull of Pipa is abnormal, being greatly flattened and 
containing little cartilage. The fronto-parietals are fused, and 
there is no sphenethmoid. The quadrates are well developed 
and the squamosals and parasphenoid differ much from those 
of other Anura. 



AND BRANCHIAL ARCHES. 

In larval Amphibia the hyoid and four branchial arches 
are generally present, and in adult Ichthyoidea they are 
frequently almost as well represented as in the larva, and 
are of use in strengthening the swallowing apparatus. They 
are very well seen in Siredon, and consist of a hyoid attached 
by ligaments to the suspensorium, followed by four branchial 
arches of which the first and second are united by a copula 
(fig. 29, D, 8), while the third and fourth are not. The hyoid 
is not always the largest and best preserved of the arches, 
for sometimes as in Spelerpes one of the branchials is far 
larger than the hyoid. Four branchial arches occur in Siren 
as in Siredon, but in Proteus there are only three. 

In some larval Labyrinthodontia (Branckiosaurus) four 
branchial arches are known to occur, and their arrangement 
is almost precisely similar to that in Siredon. 

In Gymnophiona the remains of only three branchial 
arches occur in addition to the hyoid. The four arches are 
all very similar to one another, each consists of a curved rod 
of uniform diameter throughout. The hyoid is united with 
the first branchial arch, but has no attachment to the 
cranium. 

In larval Anura (fig. 29, C) the arrangement of the 
hyoid and branchial arches is much as in Urodela. In the 
adult, however, the ventral parts of all the arches unite, form- 
ing a compact structure, the basilingual plate (fig. 29, B, 1). 



THE SKELETON IX AMPHIBIA. THE HYOID. 



181 



The dorsal parts of the first three branchial arches disappear, 
but those of the fourth become ossified and form the short, 
stout thyrohyals or posterior cornua. The dorsal parts of the 
hyoid arch in the adult form a pair of long bars, the anterior 




FIG. 29. VISCERAL ARCHES OF AMPHIBIA. 

A. Molge cristata (after PAKKEB). 

B. Rana temporaria adult (after PARKER). 

C. Tadpole of Rana (after MAKTIX ST AXOE). 

D. Siredon pisciformis (after CREDXEB). 

In each case the ossified portions are slightly shaded, while the carti- 
laginous portions are left white. 



1. basilingual plate. 

2. hyoid arch. 

3. first branchial arch. 

4. second do. 



5. third branchial arch. 

6. fourth do. 

7. thyrohyal. 

8. copula. 



182 THE VERTEBRATE SKELETON. 

cornua, which are united to the periotic region of the skull in 
front of the fenestra ovalis either by short ligaments or by 
fusion as in Eufo. In Pipa and Xenopus the first and 
second branchial arches persist as well as the fourth (thyro- 
hyal), but in Pipa the hyoid is wanting. 

RIBS. 

Ribs are generally very poorly developed in Amphibia. 
In Anura they are in most cases absent; when present they 
generally form minute unossified appendages attached to the 
transverse processes, but in Discoglossus and Xenopus the 
anterior vertebrae are provided with distinct ribs. In 
Urodela and Labyrinthodontia they are generally short 
structures, each as a rule attached to the vertebra by a 
bifurcated proximal end. The number of rib-bearing vertebrae 
varies, but the first and the posterior caudal vertebrae are 
always ribless. The anterior caudal vertebrae too are gene- 
rally ribless, but sometimes a few of them bear small ribs. 
In Spelerpes the last two trunk vertebrae are ribless, and 
hence may be regarded as lumbar vertebrae. 

In Gymnophiona ribs are better developed than in any 
other Amphibia; they occur on all the vertebrae except the 
first and last few, and are attached to the transverse processes, 
sometimes by single, sometimes by double heads. 

Sternal ribs are almost unknown in Amphibia, but traces 
of them occur in Menobranchus. 

STERNUM. 

In Amphibia the sternum is not very well developed; 
sometimes as in Gymnophiona and Proteus no traces of it 
occur, and in the Urodela it is never ossified. It is always 
very intimately related to the pectoral girdle. In the Sala- 
mandrina it has the form of a broad thin plate of cartilage, 
grooved and overlapped by the coracoid. 

In most Anura the sternum consists of a number of parts 



THE SKELETON IN AMPHIBIA. THE STERNUM. 183 

A 




FIG. 30. SHODLDEK-GIBDLE AND STERNUM OF 

A. An old male common Frog (Rana temporaries. 

B. An adult female Docidophryne gigantea (after PARKEB). 

In both A and B the left suprascapula is removed. The parts left 
unshaded are ossified ; those marked with small dots consist of hyaline 
cartilage, those marked with large dots of calcified cartilage. 

1. calcified cartilage of supra- 7. clavicle. 

scapula. 8. glenoid cavity. 

2. ossified portion of supra- 9. coracoid foramen. 

scapula. 10. episternnm. 

3. scapula. 11. omosternum. 

4. coracoid. 12. sternum. 

5. epicoracoid. 13. xiphisternum. 

6. precoracoid. 



184 THE VERTEBRATE SKELETON. 

arranged in series. At the anterior end is a flat cartilaginous 
plate with a bony basal stalk. This plate is called the epi- 
sternum, and its stalk the omosternum. The continuity of 
the sternum is now interrupted by a pair of cartilaginous 
structures, the epicoracoids, which are shoulder-girdle elements, 
and represent the unossified ventral ends of the coracoids. In 
some cases cartilaginous epiprecoracoids can also be distin- 
guished. Further back is the long sternum proper, while last 
comes the xiphisternum, a broad expanded plate of cartilage. 

In some Anura such as Pipa and Hyla the number of 
sternal elements is considerably reduced. 

APPENDICULAR SKELETON. 
PECTORAL GIRDLE. 

The most primitive Amphibian shoulder-girdle is found in 
the Urodela. It consists of a dorsal element, the scapula, 
a posterior ventral element, the coracoid, and an anterior 
ventral element, the precoracoid. The clavicle is not de- 
veloped, and the two coracoids overlap in the middle line. 
The shoulder-girdle remains largely cartilaginous but the 
proximal end of the scapula is ossified, and the ossification 
may extend through part of the coracoid and precoracoid. 

In Labyrinthodontia there is an exoskeletal ventral buckler 
formed of three plates, a median one, which probably repre- 
sents an interclavicle, and two lateral ones, which are probably 
clavicles. Traces of endoskeletal structures, probably corre- 
sponding to the precoracoid and scapula, are also known in 
some cases. The Gymnophiona and some of the Labyrintho- 
dontia have lost the pectoral girdle and limbs. 

The ossification of the shoulder-girdle has gone on much 
further in Anura than it has in Urodela. Clavicles are present 
and the scapula and coracoid of each side are ossified from 
separate centres. The distal part of the scapula forms a large 
imperfectly ossified plate, the suprascapula. 



THE SKELETON IX AMPHIBIA. ANTERIOR LIMB. 185 

The shoulder-girdle of Anura is however subject to con- 
siderable variations. In the Toads (Bufonidae) the epicora- 
coids or unossitied ventral ends of the coracoids and pre- 
coracoids overlap in the middle line (fig. 30, B, 5). This 
arrangement is called Arclferous. In the Frogs, Ranidae, 
and other forms belonging to the group Firmisternia, the 
epicoracoids do not overlap but form a narrow cartilaginous 
bar separating the ventral ends of the coracoids (fig. 30, A, 5). 

ANTERIOR LIMB. 

In many Amphibia and especially in the Urodela the 
anterior limb has a very simple unmodified arrangement. 
The humerus is straight and of moderate length, its ends are 
rounded for articulation on the one hand with the shoulder- 
girdle, and on the other hand with the radius and ulna. In 
the Urodela the radius and ulna are distinct. In the Anura 
they have fused, though the line of junction of the two 
is not obliterated. Their proximal ends are hollowed for 
articulation with the convex end of the humerus. 

The manus in all recent Amphibia agrees in never having 
more than four complete digits, but is subject to considerable 
variation, this statement applying especially to the carpus. 

In the larva of Salamandra (fig. 31, A), except that the 

pollex is absent 1 , the manus retains completely the condition 

which is generally regarded as primitive for the higher 

Vertebrata. It consists of an anterior row of three elements, 

the ulnare, intermedium, and radiale, and a posterior row 

of four, the carpalia 2, 3, 4, and 5. Interposed between the 

two rows is a cent rale. Jfenobranchus has a similar very 

i simple carpus. In most other Amphibia this simplicity is 

i lost. This loss may be due to : 

(a) fusion of certain structures, e.g. in the adult Sala- 
mandra the intermedium and ulnare have fused, 

1 The first digit present is sometimes regarded as the pollex, but from 
analogy with Anura it is probable that the pollex is the missing digit. 



186 



THE VERTEBRATE SKELETON. 



(6) displacement of structures, e.g. in Bufo viridis, the 
centrale has been pushed up till it comes to articulate with 
the radius, 

(c) the development of supernumerary elements, especially 
of extra centralia. In Megalobatrachus two or even three 
centralia sometimes occur. 




FIG. 31. A, EIGHT ANTIBRACHIUM AND MANUS OF A LARVAL SALAMAN- 
DER (Salamandra maculosa) (after GEGENBAUR). 
B, BIGHT TARSUS AND ADJOINING BONES OF Molge sp. (after 
GEGENBAUR). 

1. radius. 11. 

2. ulna. 12. 

3. radiale. 13. 

4. intermedium. 14. 

5. ulnare. 15. 

6. centrale. 16. 



7. car pale 2. 

8. 3. 

9. 4. 
10. 5. 



17. 

18. 



tibia. 

fibula. 

i 

tibiale. 

intermedium. 

fibulare. 

centrale. 

tar sale 1. 

tarsalia 4 and 5 fused. 



I. II. III. IV. V. digits. 



In the great majority of Amphibia while one digit, 
probably the first, is absent, the other four digits are well 
developed. In the forms however with degenerate limbs like 
Amphiuma, Siren and Proteus the number of digits is still 



THE SKELETON IN AMPHIBIA. PELVIC GIRDLE. 187 

further reduced. In Siren there are three or four, in Proteus 
three, and in Amphiuma two or three digits in the manus. 

In Anura the pollex is represented only by a short 
metacarpal. There are sometimes traces of a pre-pollex. 
The carpus often has two centralia and the intermedium 
is absent. 

In Labyrinthodontia the limbs are generally very simple 
and resemble those of Urodela. In some forms, however, the 
manus differs from that of all living Amphibia in possessing 
five well-developed digits. 

PELVIC GIRDLE. 

The simplest Amphibian pelvis is that of some of the 
Labyrinthodontia; thus in Mastodonsaurus it consists dorsally 
of a short broad ilium placed vertically and attached to the 
sacrum, and ventrally of a small pubis and of a large 
ischium meeting its fellow in the middle line. In some 
Labyrinthodonts the pubes as well as the ischia meet in 
a ventral symphysis, and in many there are no obturator 
foramina. In Siren, Gymnophiona and some Labyrinthodontia 
the pelvic girdle and limbs are absent. 

In Urodela the ventral element of the pelvis on each side 
forms a flat plate which meets its fellow of the opposite side. 
The anterior part of the plate, representing the pubis, gene- 
rally remains cartilaginous throughout life; the posterior 
part representing the ischium is in almost every case well 
ossified. Attached to the anterior end of the pubes there is 
an unpaired bifid cartilaginous structure, the epipubis. The 
ilia are vertically placed. 

In most Anura the pelvis is peculiarly modified in corre- 
lation with the habits of jumping. The long bone generally 
called the ilium is placed horizontally and is attached at its 
extreme anterior end to the sacrum. The ischium is ossified 
and distinct. Ventrally in front of the ischium there is a 
tract of unossified cartilage which is often regarded as the 



188 THE VERTEBRATE SKELETON. 

pubis. In Xenopus, however, the bone corresponding to the 
ilium of the Frog is seen to ossify from two centres, one 
formihg the ilium, the other, which lies at the symphysis, 
being apparently the pubis. This makes it probable that the 
so-called ilium of the Frog is really to be regarded as an ilio- 
pubis, and renders the homology of the cartilaginous part 
uncertain, but it probably corresponds to the acetabular bone 
of mammals. In Xenopus also there is a minute epipubis 
similar to that of Urodeles. 

POSTERIOR LIMB. 

In Urodela the posterior limb (fig. 31, B) closely resembles 
the anterior limb, but is even less removed from the primitive 
condition of the higher vertebrates in the fact that all five digits 
are commonly present. The tibia and fibula are short bones 
approximately equal in size. In some cases the number of 
digits is reduced. Thus in Menobranchus the pes has four 
digits, in Proteus it has two, and in Amphiumo two or three, 
while in Siren the posterior limbs have atrophied. 

In correlation with their habits of jumping, the posterior 
limbs in Anura are much lengthened and considei'ably modified. 
The tibia and fibula are completely fused. The intermedium 
is absent, while the tibiale and fibulare are greatly elongated. 
Tarsalia 4 and 5 are absent. Five- digits are always present, 
and there is a pre-hallux formed of two or more segments. 

In general the posterior limbs in Labyrinthodontia bear the 
closest resemblance to the anterior limbs ; in some cases three 
centralia are found. 

In Ichthyoidea, and in most Labyrinthodontia, the carti- 
lages of the carpus and tarsus remain unossified; in Salaman- 
drina and in Anura they are generally ossified. 



CHAPTER XIII. 
SAUROPSIDA. 

THIS great group includes the Reptiles and Birds and 
forms the second of the three into which the Gnathostomata 
may l>e divided. There is nearly always a strongly-developed 
epiblastic exoskeleton which has the form of scales or feathers, 
and in some cases a dermal exoskeleton is also well developed. 
In living forms the notochord never persists, being replaced 
by vertebrae, but in some extinct forms the centra are 
notochordal. The vertebral centra are ossified, and only in 
exceptionally rare cases have terminal epiphyses. The skull 
is well ossified and has membrane bones incorporated in its 
walls. 

The occipital segment is completely ossified, and an inter- 
orbital septum or bony partition separating the two orbits 
is usually developed to a greater or less extent. The skull 
generally articulates with the vertebral column by a single 
occipital condyle into the composition of which the ex- 
occipitals and basi-occipital enter in varying proportions. 
The pro-otic ossifies, and either remains distinct from the 
epi-otic 1 and opisthotic throughout life, or unites with them 
only after they have fused with the adjacent bones. The 
hyoid and branchial arches are much reduced ; and the 
representative of the hyomandibular is connected with the 

1 According to Baur a distinct epi-otic is not recognisable in the 
reptilian skull. 



190 THE VERTEBRATE SKELETON. 

auditory apparatus, forming the auditory ossicles 1 . Each 
ramus of the mandible always consists of a cartilage bone, 
the articular, and several membrane bones. The mandible 
articulates with the cranium by means of a quadrate. The 
ribs in Birds and some Reptiles bear uncinate processes, i.e. 
small, flat, bony or cartilaginous plates projecting backwards 
from their posterior borders. The sternum is not transversely 
segmented as in mammals, and there are commonly distinct 
cervical ribs. The ankle joint is intertarsal, or situated 
between the proximal and distal row of tarsal bones, not 
crurotarsal as in Mammalia. 



CLASS I. 

The axial skeleton is generally long, and that of the limbs 
frequently comparatively short, or sometimes absent. 

The exoskeleton generally has the form of epidermal 
scales, which are often combined with underlying bony dermal 
plates or scutes and may sometimes form a continuous armour. 
Neither feathers nor true hairs are ever present. The verte- 
bral column is generally divisible into the five usual regions. 
The centra of the vertebrae vary enormously, and may be 
amphicoelous, procoelous, opisthocoelous or flat, but they never 
have saddle-shaped articulating surfaces. The quadrate is 
always large, and is sometimes fixed, sometimes movable. 
A transpalatine bone uniting the pterygoid and maxilla is 
generally present. 

Free ribs are often borne along almost the whole length 
of the trunk and tail, and often occur attached to the cervical 
vertebrae. The sacrum is generally composed of two vertebrae 
which are united with the ilia by means of expanded ribs. 
The sternum is rhomboidal, and may either be cartilaginous 

1 H. Gadow, Phil. Trans., vol. 179, 1888. 

2 See G. Baur, J. Morph., vol. i., 1887. R. Lydekker, Catalogue of 
the Fossil Reptilia and Amphibia in the British Museum, Parts i. & n. 
C. K. Hoffmann, Peptilien, in Bronn's Classen und Ordnittt'ien <lr* Thier- 
reichs, Bd. vi., 3 abth. 187990. 



REPTILIA. THEROMORPHA. 191 

or formed of cartilage bone, but never of membrane bone ; 
it differs from that of birds also in the fact that it does not 
ossify from two or more centres. An interclavicle is generally 
present. There are always more than three digits in the 
manus, and never less than three in the pes. In all living 
reptiles the ilia are prolonged further behind the acetabula 
than in front of them, and the bones of the pelvis remain as 
a rule, distinct from one another throughout life. 

The pubes (pre-pubes) and ischia both commonly meet in 
ventral symphysis, and the acetabula are wholly or almost 
wholly ossified. The metatarsals are not ankylosed together. 

Order 1. THEROMORPHA '. 

This order includes a number of mainly terrestrial, extinct 
reptiles, which differ much from one another, and show remark- 
able points of affinity on the one hand with the Labyrintho- 
dont Amphibia, and on the other with the Mammalia. The 
vertebrae are nearly always amphicoelous and sometimes have 
notochordal centra. The skull is short and has the quadrate 
immovably fixed. There is an interparietal foramen, and gene- 
rally large supratemporal fossae bounded by supratemporal 2 
arcades, but with no infratemporal 2 arcades; Elginia however 
has the whole of the temporal region completely roofed over. 

The teeth are placed in distinct sockets and are very 
variable in form, the dentition sometimes resembling the 
heterodont dentition of mammals. The humerus has distinct 
condyles and an ent-epicondylar foramen 3 as in many mammals. 

The pubis is fused with the ischium, and both pectoral and 
pelvic girdles are remarkably solid. The obturator foramen 

1 T. H. Huxley, Quart. J. Geol. Soc., vol. xv. p. 649, 1859. R. Owen, 
Catalogue of Fossil Reptiles of S. Africa in the British Museum, London, 
1876. H. G. Seeley, various papers published in the P. R. Soc. London, 
and Phil. Trans. 

- See pp. 281283. 

3 An ent-epicondylar foramen is one piercing the humerus on its 
inner side just above the condyle. 



192 THE VERTEBRATE SKELETON. 

is remarkably small or even absent. The anterior ribs have 
two articulating surfaces, and each articulates by its tuber- 
culum with the transverse process, and by its capitulum with 
the centrum as in mammals. 

These reptiles occur chiefly in deposits of Triassic and 
Permian age. Some of the best known genera are Dicynodon, 
Udenodon, Placodus, Pariasaurus and Galesaurus. They will 
be noticed in the general account of the skeleton in reptiles. 

Order 2. SAUROPTEKYGIA. 

This order includes a number of extinct marine reptiles, 
devoid of an exoskeleton. The tail is short, the trunk long, 
and the neck in the most typical forms extremely long. The 
vertebrae have slightly biconcave, or nearly flat centra. The 
skull is relatively small and has large supratemporal fossae. 
The teeth are placed in distinct sockets, and are generally 
confined to the margins of the jaws ; they are sharp and 
curved and are coated with grooved enamel. The premaxillae 
are large, and there is an interparietal foramen. The quadrate 
is firmly united to the cranium. The anterior nares are 
separate and are placed somewhat close to the orbits. There 
is no ossified sclerotic ring. The palatines and pterygoids 
meet the vomers, and more or less completely close the palate, 
and in some forms, e.g. Plesiosaurus, there is a distinct para- 
sphenoid. Thoracic ribs are strongly developed and each 
articulates with its vertebra by a single head. The cervical 
vertebrae have well-marked ribs, which articulate only with 
the centra, in this respect differing from those of Crocodiles. 
The caudal vertebrae bear both ribs and chevron bones, and 
abdominal splint-ribs are largely developed. 

In the shoulder-girdle the coracoids are large and meet in a 
ventral symphysis ; precoracoids and a sternum are apparently 
absent, but parts generally regarded 1 as the clavicles and 

1 According to Hulke they should be regarded as the omosternum, 
the clavicles and interclavicle being wanting. 



REPTILU. CHELOXIA. 193 

nterclavicle are well developed. In tKe pelvis, the pubes and 
schia meet in a long symphysis. The limbs are pentedactvlate. 
ind in the best known forms, the Plesiosauridae, form swim- 
ning paddles. 

The Sauropterygia occur in beds of Secondary age, and 
ome of the best known genera are Phsio8auru&, Pliosaurus 
md 



Order 3. CHELOXIA. 

In the Tortoises and Turtles the body is 'enclosed in a bony 
lx>x. formed of the dorsal carapace, and a flat ventral buckler, 
the plastron. Except in Dermochelys the carapace is partly 
f ormed from the vertebral column and ribs, partly from dermal 
Both carapace and plastron are, except in Dermo- 
Trionyx and their allies, covered with an epidermal 
exoskeleton of horny plates, which are regularly arranged, 
though their outlines do not coincide with those of the under- 
lying bones. The thoracic vertebrae have no transverse pro- 
cesses, and are quite immovably fixed, but the cervical and 
caudal vertebrae are very freely movable. There are no lumbar 
vertebrae. The skull is extremely solid, and frequently has a 
very complete false roof. Teeth have been detected in embryos 
<>f Trionyx but with this exception the jaws are toothless, 
and are encased in horny beaks. The quadrate is firmly 
fixed. The facial part of the skull is very short, and the 
alisphenoidal and orbitosphenoidal regions are unossified. In 
living forms there are no separate nasal bones, while large 
prefrontals and postfrontals are developed. There is a com- 
paratively complete bony palate chiefly formed of the palatines 
and pterygoids. The anterior nares are united and placed at 
the anterior end of the skull, and the premaxillae are very 
small. There is no transpalatine bone and the vomer is 
unpaired. The dentaries are generally fused together. 

There are ten pairs of ribs, and each rib has only a single 
R- 13 



194 THE VERTEBRATE SKELETON. 

head and is partially attached to two vertebrae ; there are no 
cervical or sternal ribs. There is no true sternum. 

The three anterior elements of the plastron are respectively 
homologous with the interclavicle and two clavicles of other 
reptiles, while the remaining elements of the plastron are pro- 
bably homologous with the abdominal ribs of Crocodiles. The 
pectoral girdle lies within the ribs, and the precoracoids and 
coracoids do not meet in ventral symphyses. The scapula and 
precoracoid are ossified continuously. The pubis probably 
corresponds with the prepubis of Dinosaurs. There are four 
limbs each with five digits. 

The order includes three suborders : 

Suborder (1). TRIONYCHIA. 

The carapace and plastron have a rough granular surface 
covered with skin and without any horny shields. 

The plastron is imperfectly ossified, and marginal bones 
may be absent, or if present are confined to the posterior 
portion of the carapace. The pelvis is not united to the 
plastron. The cranium has not a complete false roof and the 
head can be drawn back under the carapace. 

The first three digits of both manus and pes bear claws, 
and the fourth digit in each case has more than three pha- 
langes. The most important genus is Trionyx. 

Suborder (2). CRYPTODIRA. 

The carapace and plastron vary in the extent to which they 
are ossified, and except in Dermochelys 1 and its allies are 
covered by horny plates. Marginal bones are always present. 
The head can generally be drawn back under the carapace. 
The pelvis is not firmly united to the plastron. The cranium 
often has a complete false roof, and in the mandibular articu- 
lation the cup is borne by the cranium, and the knob by the 
mandible. Among the more important genera are Dermo- 
cJielys, Ckelone, and Testudo. 

1 See p. 272. 



REPTILIA. ICHTHYOSAURIA. 195 

Suborder (3). PLEURODIRA. 

The carapace and plastron are strongly ossified, and firmly 
united to the pelvis. The head and neck can be folded late- 
rally under the carapace, but cannot be drawn back under it. 
The cranium has a more or less complete false roof, and in the 
mandibular articulation the knob is borne by the cranium, and 
the cup by the mandible. Chelys is a well-known genus. 

Order 4. ICHTHYOSAURIA l . 

The order includes a number of large extinct marine 
reptiles whose general shape is similar to that of the Cetacea. 
The skull is enormously large, and the neck short. The tail 
is very long, and is terminated by a large vertically-placed 
bilobecl fin, the vertebral column running along the lower 
lobe. The very numerous vertebrae are short and deeply bi- 
concave. The vertebral column can be divided into caudal 
and precaudal regions only, as the ribs which begin at the 
anterior part of the neck are continued to the posterior end 
of the trunk without being connected with any sternum or 
sacrum. The precaudal vertebrae bear two surfaces for the 
articulation of the ribs, while in the caudal vertebrae the 
two surfaces have coalesced. The caudal region is also 
distinguished by its chevron bones. The vertebrae have 
no transverse processes, and the neural arches are not 
firmly united to the centra, and have only traces of zyga- 
pophyses. The atlas and axis are similar to the other 
vertebrae, but there is a wedge-shaped intercentrum be- 
tween the atlas and the skull, and another between the 
atlas and the axis. The skull is greatly elongated (fig v 32) 
and pointed, mainly owing to the length of the premaxillae. 
The orbits are enormous, and there is a ring of bones in the 
sclerotic (fig. 32, 15). The anterior nares are very small ; and 

1 E. Lydekker, Nat. Sci. vol. i. p. 514, 1892. Further references are 
there given. 

132 



196 



THE VERTEBRATE SKELETON. 



are placed far back just in front of the orbits. There is an 
interparietal foramen, and the supratemporal fossae (fig. 32, 9) 



9 13 




FIG. 32. LATERAL (BELOW) AND DORSAL (ABOVE) VIEWS or THE SKULL OF 
AN Ichthyosaurus. (Modified from Deslongchamps.) 



1. premaxilla. 

2. maxilla. 

3. nasal. 

4. prefrontal 1 . 

5. frontal. 

6. postfrontal 3 . 

7. anterior nares. 

8. orbit. 

9. supratemporal fossa. 

10. interparietal foramen. 

11. parietal. 



12. squamosal. 

13. supratemporal. 

14. quadratojugal. 

15. sclerotic ring. 

16. postorbital. 

17. jugal. 

18. lachrymal. 

19. dentary. 

20. articular. 

21. angular. 



are very large, while there are no infratemporal fossae. An 
epipterygoid occurs. The quadrate is firmly fixed to the 
cranium, and there is a large parasphenoid. There are large 
prefrontals, but the frontals are very small. The very numer- 
ous teeth are large and conical, and are placed in continuous 



1 The exact position of the suture between the prefrontal and post- 
frontal is not known. 



REPTILIA. ICHTHYOSAURIA. 197 

grooves without being ankylosed to the bone. They are 
confined to the jaw-bones. 

The ribs are long, and the anterior ones have capitula and 
tubercula. There is no sternum, but the ventral body wall 
is strengthened by a complex system of abdominal splint ribs. 

The pectoral girdle is strongly developed, the scapulae are 
narrow, the coracoids broad, and meet ventrally without over- 
lapping. There are probably no precoracoids, but clavicles 
and a T-shaped interclavicle are well developed. 

The limbs are very short, and completely modified into 
swimming paddles. The humerus and femur are both short, 
while the radius and ulna, tibia and fibula are generally still 
further reduced to the form of short polygonal bones. 

The digits are formed of longitudinal series of very numer- 
ous small bones. The number of digits is five, but there 
sometimes appear to be more owing to the bifurcation of 
certain of them, or to the addition of marginal bones, either 
to the radial or ulnar side of the limb. The humerus has no 
foramen, and both humerus and femur are unique in that 
they are distally terminated by concave surfaces instead of 
by convex condyles. The pelvic limb is much smaller than 
the pectoral. The pelvis has no bony connection with the 
vertebral column, and all the component bones are small and 
rod-like. 

The Ichthyosauria are confined to beds of Secondary age 
and by far the best known genus is Ichthyosaurus. 

Order 5. RHYXCHOCEPHALIA. 

This order includes the living Sphenodon (Hatteria) and 
various extinct forms. The general shape of these animals is 
lizard-like and the tail is long. 

The vertebrae are amphicoelous or sometimes nearly flat, 
and the notochord sometimes persists to some extent. Protero- 
saurus differs from the other members of the order in having 
opisthocoelous cervical vertebrae. 



198 THE VERTEBRATE SKELETON. 

The sacrum is composed of two vertebrae. Ossified inter- 
centra (interdorsalia) generally occur in the cervical and 
caudal regions, and sometimes throughout the whole vertebral 
column. In the skull the quadrate is immovably fixed and 
united to the pterygoid. The palate is well ossified, while 
the premaxillae which are often beak-like are never ankylosed 
together. The jaws may be toothless or may be provided 
with teeth which are usually acrodont (see p. 199). The 
palatines frequently bear teeth, and in Proterosaurus teeth 
occur also on the pterygoids and vomers. The rami of the 
mandible are united by ligament at the symphysis except in 
the Rhynchosauridae, in which the union is bony. Superior 
and inferior temporal arcades occur. 

The ribs have capitula and tubercula, and often uncinate 
processes (see p. 190) as in birds. A pectoral girdle and 
sternum, with clavicles and a T-shaped interclavicle are de- 
veloped, and abdominal ribs are always found. The precoracoid 
is however absent. The limbs are pentedactylate. 

Sphenodon 1 (Hatteria) now living in some of the islands 
of the New Zealand group, is certainly the most generalised 
of all living reptiles. Though lizard-like in form it differs 
from all living lizards in the possession of two temporal 
arcades, abdominal ribs and a fixed quadrate ; and is often 
considered to be nearly allied in many respects to the type 
of reptile from which all the others took their origin. 

Among the better known extinct forms are Proterosaurus 
of Permian and Hyperodapedon of Triassic age. 

Order 6. SQUAMATA. 

This order includes the extinct Mosasaurians, and the 
lizards and snakes which form the vast majority of living 
reptiles. The trunk may be moderately elongated and provided 

1 A. Gtinther, On the Anatomy of Hatteria, Phil. Tram. vol. 157, 1867, 
p. 595. 



REPTILIA. SQUAMATA. 199 

with four short limbs as in lizards, or it may be limb- 
less, extremely elongated, and passing imperceptibly into 
the tail. The surface is generally completely covered with 
overlapping horny epidermal scales, below which bony dermal 
scutes may be developed. 

The vertebrae are precocious, rarely amphicoelous. There 
are no intercentra, and the neural arches are firmly united to 
the centra. Additional articulating surfaces, the zygosphenes 
and zygantra, are often developed 1 . The sacrum is formed 
of two or rarely three vertebrae, or may be wanting as in 
Ophidia. In the skull an infratemporal arcade forming the 
lower boundary of the infratemporal fossa is absent, and the 
quadrate, except in the Chamaeleons, is movably articulated 
to the squamosal. The palatal vacuities are large and the 
nares are separate. There is often a distinct parasphenoid. 
The teeth are either acrodont (i.e. ankylosed to the summit 
of the jaw), or pleurodont, i.e. ankylosed to the inner side 
of the jaw. The thoracic ribs each have a single head 
which articulates with the centrum of the vertebra ; while 
uncinate processes and abdominal ribs never occur. 

A pectoral girdle and sternum may be present, or may be 
completely absent as in snakes. Except in snakes there are 
generally four pentedactylate limbs which may either form 
paddles or be adapted for walking. 



Stiborder (1). 

The body is elongated, and as a rule four short pentedacty- 
late limbs are present, but sometimes limbs are vestigial or 

1 Zygosphenes are extra articulating surfaces borne upon the anterior 
face of the neural arch ; they fit into corresponding structures, the 
zygantra. which are borne on the posterior surface of the neural arch 
of the preceding vertebra. Ordinary zygapophyses always accompany 
them. 

- See E. D. Cope, P. Amer. Phil. Soc. vol. xxx. p. 185. 



200 THE VERTEBRATE SKELETON. 

absent. The exoskeleton generally has the form of horny 
plates, spines, or scales ; while sometimes as in the Chamae- 
leons and Amphisbaenians it is absent. In other forms such 
as Tiliqua and /Scincus, the body has a complete armour of 
bony scutes, whose shape corresponds with that of the over- 
lying horny scales. 

The vertebrae are procoelous, rarely as in the Geckos 
amphicoelous ; they are usually without zygosphenes and 
zygantra, but these structures occur in the Iguanidae. The 
sacral vertebrae of living forms are not ankylosed together, 
and the caudal vertebrae usually have well-developed chevron 
bones. 

In the skull 1 the orbits are separated from one another, 
only by an imperfectly developed interorbital septum, the 
cranial cavity not extending forwards between them, while 
the alisphenoidal region is unossified. The premaxillae may 
be paired or united (Amphisbaenidae), and there is usually 
an interparietal foramen. There may be a complete supra- 
temporal 2 arcade bounding the lower margin of the supra- 
temporal fossa, or the supratemporal fossa may be open below. 
The quadratojugal is not ossified, and the quadrate articulates 
with the exoccipital. There is no infratemporal arcade. There 
is commonly a rod like epipterygoid 3 (fig. 33, 14) connecting 
the pterygoid and parietal. 

Teeth are always present, and may be confined to the 
jaws or may be developed also on the pterygoids and rarely 
on the palatines ; they are either acrodont or pleurodont. 
The rami of the mandible are suturally united. 

A pectoral girdle is always present, and generally also a 
sternum. Clavicles and a T-shaped interclavicle are commonly 
present, but are absent in the Chamaeleons. 

1 See W. K. Parker, Phil. Trans, vol. 170, 1879, p. 595. 

'-' See p. 281. 

:i Often called the columella cranii. 



REPT1LIA. LACERTILIA. 

19 20 
8 
9 7 



201 




33. A, LATEBAL VIEW, AND 
OF A LIZAED (Yaranus 

1. premaxilla. 

2. maxilla. 

3. nasal. 

4. lateral ethmoid. 

5. supra-orbital. 

6. lachrymal. 

7. frontal. 

8. postfrontal. 

9. prefrontal. 

10. basisphenoid. 

11. pro-otic. 

12. epi-otic. 

13. pterygoid. 

14. epipterygoid (columella 

cranii). 

15. jugal. 



B, LONGITUDINAL SECTION OF THE SKCLL 

varius). xi. (Brit. Mus.) 

16. transpalatine. 

17. parasphenoid. 

18. quadrate. 

19. parietal. 

20. squamosal. 

21. supra temporal. 

22. exoccipital. 

23. dentary. 

24. splenial. 

25. supra-angular. 

26. angular. 

27. coronoid. 

28. articular. 

29. vomer. 

30. basi-occipital. 

31. orbitosphenoid. 



202 THE VERTEBRATE SKELETON. 

There is no separate precoracoid but a precoracoidal pro- 
cess (fig. 34, 7) of the coracbid is generally prominent. 




FIG. 34. LATERAL VIEW OF THE SHOULDEB-GIRDLE OF Varanus. x f . 
(Brit. Mus.). 

1. suprascapula. 5. clavicle. 

2. scapula. 6. interclavicle. 

3. glenoid cavity. 7. precoracoidal process. 

4. coracoid. 

Sternal ribs are present in chamaeleons and scinks. The 
limbs are in the great majority of cases pentedactylate and 
tha digits are clawed. The phalanges articulate by means 
of condyles. Sometimes one or both pairs of limbs are 
absent. When the posterior limbs are absent the pelvis is 
also wanting, though the loss of the anterior limbs does not 
lead to a corresponding loss of the pectoral girdle. 

The pubis corresponds to the prepubis of Dinosaurs, and 
both pubes and ischia meet in ventral symphyses. 

The suborder includes the Lizards, Chamaeleons and Am- 
phisbaenians. 

Suborder (2). OPHIDIA'. 
The Ophidia or snakes are characterised by their greatly 

1 See C. K. Hoffmann, in Bronn's Klassen und Ordnungen des 
reichs, Bd. vi., 3 abth. 188590. 



REPTILIA. OPH1DIA. 203 

elongated body and want of limbs. The body is covered with 
overlapping horny scales and bony dermal scutes are never 
present. The vertebrae are procoelous, and are distinguishable 
into two groups only, precaudal or rib-bearing, and caudal or 
ribless. The atlas vertebra is also ribless. The neural arches 
are always provided with zygosphenes and zygantra. Many 
of the vertebrae have strong hypapophyses, and the caudal 
vertebrae are without chevron bones. 

In the skull the cranial cavity extends forwards between 
the orbits, and is closed in front by downgrowths from the 
frontals and parietals which meet the well-ossified alisphenoids 
and orbitosphenoids 1 . The cranium is strongly ossified, and 
there are no parotic processes or interparietal foramen. There 
are no temporal arcades and no epipterygoid. The premaxillae 
if present are very small (fig. 51, 1) and usually toothless. 
The quadrates articulate with the squamosals, and do not as 
in Lacertilia meet the exoccipitals. The palatines do not 
unite directly with the vomers or with the base of the cranium, 
and the whole palato-maxillary apparatus is more loosely con- 
nected with the cranium than it is in Lacertilia. The ptery- 
goids, and in most cases also the palatines, bear teeth. The 
dentition is acrodont, and the rarni of the mandible are united 
only by an elastic ligament an important point serving to 
distinguish the Ophidia from the Lacertilia. There is an 
imperfectly developed interorbital septum, the ventral part 
of which is formed by the paraspheiioid. The postfrontal is 
generally well developed, while the jugals and quadratojugals 
are absent. There are never any traces of the anterior limbs 
or pectoral girdle, but occasionally there are vestiges of a 
pelvis and posterior limbs. 

1 Some anatomists consider that the closing in of the brain case in 
front is entirely due to the frontals and parietals. 



204 THE VERTEBRATE SKELETON. 

Suborder (3). PYTHONOMORPHA'. 

This suborder includes Mosasaurus and its allies, a group 
of enormous extinct marine reptiles found in beds of Cre- 
taceous age. 

The skin is in most forms at any rate unprovided with 
dermal scutes. The vertebrae may be with or without zygo- 
sphenes and zygantra. The skull resembles that of lizards, 
having an interparietal foramen, and a cranial cavity open 
in front. The squamosal takes part in the formation of the 
cranial wall, and the quadrate articulates with the squamosal, 
not as in Lacertilia with the exoccipital. There are large 
supratemporal fossae, bounded below by supratemporal arcades. 
The teeth are large and acrodont, and occur on the pterygoids 
as well as on the jaws. The two rami of the mandible are 
united by ligament only. Pectoral and pelvic girdles are 
present, but clavicles are wanting, and the pelvis is not as a 
rule united to any sacrum. 

The limbs are pentedactylate, and are adapted for swim- 
ming, while all the limb bones except the phalanges are rela- 
tively very short. The number of phalanges is not increased 
beyond the normal, and they articulate with one another by 
flat surfaces. The terminal phalanges are without claws. 

Order 7. DiNOSAURiA 2 . 

The extinct reptiles comprising this order were all terres- 
trial, and include the largest terrestrial animals known. They 

1 E. D. Cope, Rep. U. S. Geol. Surv., 1875, vol. ir., The vertebrata 
of the Cretaceous formations of the west. E. D. Cope, P. Boston Soc. 
1862, xn. p. 250. 0. C. Marsh, Amer. J. Set. 1872, vol. 3. R. Owen, 
Quart. J. Geol. Soc. 1877, and 1878. 

2 J. W. Hulke, Presidential address to tJie Geol. Soc. of London, 
1883 and 1884. 0. C. Marsh, many papers in the Amer. J. Sci. from 
1878 onwards, also in the Geol. Hag. R. Owen, History of British 
fossil reptiles : Dinosauria (Palaeont. Soc.). 



REPTILIA. DIXOSAURIA. 205 

vary greatly in size and in the structure of the limbs, some 
approach close to the type of structure met with in birds, 
others are allied to crocodiles. 

Passing to the more detailed characters : there is some- 
times a well-developed exoskeleton having the form of bony 
plates or spines. The vertebrae may be solid or their centra 
may be hollowed internally ; their surfaces may be flat, bi- 
concave or opisthocoelous. The sacrum is composed of from 
two to six vertebrae. 

As regards the skull, the quadrate is large and fixed, and 
suprateaiporal and infratemporal fossae bounded by bone occur. 
The teeth are more or less laterally compressed, and often 
have serrated edges ; they may be placed in distinct sockets 
or in a continuous groove. The ribs have capitula and tuber- 
cula, and sternal ribs often occur. The scapula is very large, 
the coracoid small, and there is no precoracoid, or T-shaped 
interclavicle. Clavicles are only known in a few cases. In 
the pelvis the ilium is elongated both in front of, and behind, 
the acetabulum, sometimes the pre-pubis, sometimes the post- 
pubis is the better developed. The anterior limbs are shorter 
than the posterior, and the long bones are sometimes solid, 
sometimes hollow. 

There are three well-marked suborders of the Dinosauria. 

Suborder (1). SAUROPODA 1 . 

The reptiles belonging to this group were probably quadru- 
pedal and herbivorous. 

They have the cervical and anterior trunk vertebrae 
opisthocoelous, while the posterior vertebrae are biconcave; 
all the presacral, and sometimes the sacral vertebrae are 
hollowed internally. The teeth are spatulate and without 
serrated edges, they are always planted in distinct sockets, 
and some of them are borne by the premaxillae. 

1 The diagnostic characters of the different groups of Dinosaurs are 
in the main those given by von Zittel. 



206 



THE VERTEBRATE SKELETON. 




REPTILIA. DINOSAURIA. 207 

1. anterior nares. o. scapula. 

2. prominence on the nasal 6. coracoid. 

bones which probably 7. ilium. 

carried a horn. 8. pubis (pre-pubis). 

3. pre-orbital vacuity. 9. ischium. 

4. orbit. 

The nares have the form of long slits and there are large 
pre-orbital vacuities. 

The limb bones are solid, and the anterior limbs are not 
much shorter than the posterior ones. All the limbs are 
plantigrade and pentedactylate, and the digits of the pes are 
clawed. There is a large pre-pubis directed downwards and 
forwards, meeting its fellow in a ventral syrnphysis, but there 
is no post-pubis. 

The Sauropoda are found in the secondary rocks of Europe 
and X. America and include the largest land animals that are 
known to have existed. Many of the best known forms such 
as Brontosaurus and Morosaurus are Xorth American. 



Stiborder (2). THEROPODA. 

The members of this suborder were all carnivorous, and 
from the small comparative size of the anterior limbs many of 
them were probably bipedal. 

The vertebrae are opisthocoelous or amphicoelous, their 
neural arches are provided with zygosphenes and zygantra, 
and their centra are frequently hollowed internallv ; the limb 
bones are also hollow, and in fact the whole skeleton is ex- 
tremely light. The tail is of great length. The teeth are 
pointed and recurved, arid have one or both borders serrated ; 
they are always planted in distinct sockets, and some of them 
are borne by the premaxillae. There are large pre-orbital 
vacuities. The digits of both manus and pes are terminated 
by pointed ungual phalanges which must have borne claws. 
In the pelvis the pre-pubes and ischia are slender bones, the 



208 THE VERTEBRATE SKELETON. 

former meeting in a ventral symphysis. The ilia are very 
deep vertically and there are no post-pubes. The astragalus 
is closely applied to the tibia, in front of which it sends an 
ascending process, sometimes the two bones appear to have 
been ankylosed together, as in birds. The metatarsals are 
elongated and the feet digitigrade. 

The Theropoda vary greatly in size, one of the best known 
genera Compsognathus was about as large as a cat, another, 
Megalosaurus, perhaps as large as an elephant. Ceratosaurus 
is the name of a well-known North American form regarded 
by many authorities as identical with Megalosaurus. 

Suborder (3). ORTHOPODA. 

This suborder includes the most specialised of the Dino- 
saurs, certain of which resemble the Theropoda in being 
bipedal. In some of them such as Stegosaurus the exoskeleton 
is strongly developed, in others such as Iguanodon it is 
absent. 

The vertebrae are solid and may be opisthocoelous, bi- 
concave, or flat. The teeth are compressed and serrated, 
often irregularly, and are frequently not set in distinct sockets. 
The anterior part of the premaxillae is without teeth, and a 
toothless pre-dentary or mento-meckelian bone is present. 
The pre-orbital vacuities are small or absent, and the nares 
are large and placed far forwards. 

The most characteristic features of the group are found 
in the pelvis which, except in the Ceratopsia, bears a striking 
resemblance to that of birds. The ischium and post-pubis 
are long slender bones directed backwards parallel to one 
another, and the pre-pubis is also well developed. The ischium 
has an obturator process. The limb bones are sometimes 
hollow, sometimes solid. The anterior limbs are much shorter 
than the posterior, pointing to a bipedal method of progression. 
The pes is digitigrade or plantigrade, and has three, rarely four, 
digits. 



REPTILIA. DINOSAURIA. 209 

The suborder Orthopoda may be further subdivided into 
three sections : 

A. STEGOSAUKIA. 

A dermal exoskeleton is strongly developed. The verte- 
bral centra are flat or biconcave, and neither they nor the 
limb bones are hollowed out by internal cavities. The limbs 
are plantigrade, the anterior ones short, the posterior ones 
very large and strong. The post-pubis is well developed ; 

e.g. Stegosaurus from the Upper Jurassic of Colorado. 

B. CERATOPSIA. 

There is sometimes a well-developed dermal exoskeleton 
formed of small granules and plates of bone. The bones are 
solid, and the vertebral centra flat. The cranium bears a 
pair of enormous pointed frontal horns, and the parietal is 
greatly expanded and elevated behind, forming with the 
squamosals a shield which overhangs the anterior cervical 
vertebrae. The premaxillae are united, and in front of them 
is a pointed beak-like bone which bites upon a toothless 
predentary ossification of the mandible. The teeth have two 
roots. The anterior limbs are but little shorter than the 
posterior ones. There is no post-pubis ; 

e.g. Polyonax from the uppermost Cretaceous of Montana. 

C. C-RXITHOPODA 1 . 

There is no dermal exoskeleton. The cervical vertebrae 
are opisthocoelous, and so are sometimes the thoracic. The 
limb bones are hollow and the anterior limbs are much shorter 
than the posterior ones. The feet are digitigrade and pro- 
vided with long pointed claws. The post-pubis is long and 
slender and directed back parallel to the ischium ; 

e.g. Iguanodon from the European Cretaceous. 

1 See 0. C. Marsh, Amer. J. Sci. (3), vol. 48, 1894, p. 85. 
R. 14 



210 THE VERTEBRATE SKELETON. 

Order 8. CROCODILIA'. 

This order includes the Crocodiles, Alligators and Garials 
and various extinct forms, some of which are closely allied to 
the early Dinosaurs. 

There is always a more or less complete exoskeleton formed 
of bony scutes overlain by epidermal scales ; these bony scutes 
are specially well developed on the dorsal surface but may 
occur also on the ventral. The vertebral column is divisible 
into the five regions commonly distinguishable. In all living 
forms the vertebrae, with the exception of the atlas and axis, 
the two sacrals, and first caudal, are procoelous, but in many 
extinct forms they are amphicoelous. The atlas (fig. 71) is 
remarkable, consisting of four pieces, and the first caudal is 
biconvex. 

The teeth are, in the adult, planted in separate deep 
sockets. The skull is very dense and solid, and all the 
component bones including the quadrate are firmly united. 
The dorsal surface of the skull is generally characteristically 
sculptured. There is an interorbital septum, and the orbito- 
sphenoidal and presphenoidal regions are imperfectly ossified. 
Supratemporal, infratemporal, and post-temporal fossae occur, 
but no interparietal foramen. In living genera there is a long 
secondary palate formed by the meeting in the middle line of 
the palatines, pterygoids and maxillae (fig. 43, A). 

Cervical ribs (fig. 41,8 and 9) are well developed, and arti- 
culate with rather prominent surfaces borne on the neural 
arches and centra respectively. The thoracic ribs articulate 
with the long transverse processes, and sternal ribs and 

1 See C. B. Briihl, Das skelet der Krokodiliden, Wien, 1862. C. K. 
Hoffmann in Bronn's Klassen iind Ordmmgen des Thier-reichs, Bd. vi. 
Abth. in. 188185. T. H. Huxley, Proc. Linn. Soc. (Zoology) 1860 
vol. iv. p. 1. B. Owen, History of Hritixk fossil Reptiles. Crorotliliti 
(Palaeont. Soc.). A. Smith Woodward, Geol. Mag. 1885, 3rd dec. n. p. 
496. A. Smith Woodward, Proc. of Geologists' Assoc. vol. ix. p. 288, 1886. 



REPTILIA. CROCODILIA. 211 

abdominal splint ribs (fig. 46, 4) occur. The sternum is carti- 
laginous, and both it and the shoulder-girdle are very simple. 
The precoracoid is represented by merely a small process on 
the coracoid, while the clavicles are absent, except in the 
Parasuchia. In the pelvis (fig. 49) there is a large ilium, and 
an ischium meeting its fellow in a ventral symphysis ; these 
two bones form almost the whole of the acetabulum. In 
front of the acetabulum, in the Eusuchia, projects a bone 
which is generally called the pubis, but is in reality rather 
an epipubis (fig. 49, 4), the true pubis being probably repre- 
sented by a fourth element which remains cartilaginous for 
some time, and later on ossifies and attaches itself to the 
ischium. The limbs are small in proportion to the size of the 
body, and are adapted for swimming or for shuffling along the 
ground ; they are plantigrade and the bones are all solid. 
In living forms the anterior limbs have five digits and the 
posterior four, the fifth being represented only by a short 
metatarsal. The first three digits in each case are clawed. 
The calcaneum has a large backwardly-projecting process. 

The order Crocodilia may be subdivided into two sub- 
orders. 

Suborder (1). PARASUCHIA. 

The vertebral centra are flat or biconcave. The pre- 
maxillae are very large, and the nares are separated, and 
placed far back. The posterior narial openings lie compara- 
tively far forward between the anterior extremities of the 
palatines. 

The palatines and pterygoids do not form a secondary 
palate. The supratemporal fossae are small, and open poste- 
riorly, the lateral temporal fossae are very large. The parietals 
and frontals are paired. Clavicles are present. The best 
known and most important genus of these extinct crocodiles 
is Belodon. 

142 



212 THE VERTEBRATE SKELETON. 

Suborder (2). EUSUCHIA. 

The vertebrae are either biconcave or procoelous. The pre- 
maxillae are small, and the anterior nares are united and 
placed far forwards. The posterior nares lie far back, the 
palatines and in living genera the pterygoids, meeting in the 
middle Hue, and giving rise to a closed palate. The supra- 
temporal fossae are surrounded by bone on all sides, and the 
parietals, and often also the frontals are united. There are 
no clavicles. The suborder includes the genera Crocodilus, 
Alligator, Garialis and others living and extinct. 

Order 9. PTEROSAURiA 1 . 

These animals, called also the pterodactyles or Ornitho- 
sauria, are a group of extinct reptiles, whose structure has 
been greatly modified from the ordinary reptilian type for the 
purpose of flight. 

The skin was naked and they vary greatly in size and in 
the length of the tail. The vertebrae and limb bones are 
pneumatic just as in birds. The presacral vertebrae are pro- 
coelous and have their neural arches firmly united to the 
centra. The neck is long, the caudal vertebrae are amphi- 
coelous, and from three to five vertebrae are fused together 
in the sacral region. The skull is large and somewhat bird- 
like, the facial portion being much drawn out anteriorly, and 
the sutures being obliterated. It resembles that of other 
reptiles in having large supratemporal fossae ; large pre-orbital 
vacuities also occur. The jaws may be toothed or toothless, 
and the teeth, when present, are imbedded in separate sockets. 
The premaxillae are large, and the quadrate is firmly attached 
to the skull. The rami of the mandible are united at the 

1 See H. G. Seeley On the Organisation of the Ornithosauria, Journ. 
Linn. Soc. (Zoology) vol. xnr. p. 84. K. A. Zittel, Ueber Flugsaurier aus 
dem lithographischen schiefer, Palaeontoijraph. xxix. p. 49. 



KEPTILIA. PTEROSAURI A. 213 

symphysis, and there is an ossified ring in the sclerotic. The 
occurrence of a postfrontal and its union with the jugal 
behind the orbit, are characteristic reptilian features. 

The ribs have capitula and tubercula, and sternal and 
abdominal ribs occur. The sternum has a well-developed keel, 
and the scapula and coracoid are large and bird-like. There 
are no clavicles or interclavicle. 

The anterior limbs are modified to form wings by the great 
elongation of the fifth digit, to which a membrane was at- 
tached. The second, third and fourth digits are clawed and 
are not elongated in the way that they are in bats. The 
pollex, if present at all, is quite vestigial. 

The pelvis is weak and small, and though the ilia are pro- 
duced both in front of and behind the acetabula, in other 
features the pelvis is not bird-like. The ischia are short and 
wide, and the pubes are represented only by the pre-pubes. 
The posterior limbs are small and the fibula is much reduced. 
The pes is quite reptilian in type, and has five separate slender 
metatarsals. The two best known genera are Pterodactylus, in 
which the tail is short, and Rhamphorhynchus, in which it is 
long. The Pterosauria are found throughout the Jurassic and 
Cretaceous formations in both Europe and North America. 



CHAPTER XIV. 

THE SKELETON OF THE GREEN TURTLE. 

(Chelone midas.) 

THE most striking feature as regards the skeleton of the 
Turtle is that the trunk is enveloped in a bony box, the dorsal 
portion of which is called the carapace, while the ventral 
portion is the plastron. 

I. EXOSKELETON. 

a. The epidermal exoskeleton in the Green Turtle as 
in all other Chelonia except Dermochelys, Trionyx and their 
allies is strongly developed, its most important part consisting 
of a series of horny shields which cover over the bony plates 
of the carapace and plastron but do not at all correspond to 
them in size and arrangement. 

The shields covering over the carapace consist of three 
rows of larger central shields, five (vertebral) shields being 
included in the middle row and four (costal) in each lateral 
row, and of a number of smaller marginal shields. 

Of the marginal shields, that lying immediately in front of 
the first vertebral is termed the nuchal, while the two suc- 
ceeding the last vertebral are called sometimes pygal, some- 
times supracaudal ; the remainder are the marginal shields 
proper. 

The epidermal covering of the plastron consists princi- 
pally of six pairs of symmetrically arranged shields, called 



THE SKELETON OF THE TURTLE. THE CARAPACE. 215 

respectively the gular, humeral, pectoral, abdominal, 
femoral, and anal, the gular being the most anterior. In 
front of the gular shields is an unpaired intergular, and 
the shields of the plastron are connected laterally with those 
of the carapace, by five or six pairs of rather irregular infra- 
marginal shields. Smaller horny plates occur on other parts 
of the body, especially on the limbs and head. 

Two other sets of structures belong also to the epidermal 
exoskeleton, viz. (a) horny beaks with denticulated edges 
which ensheath both upper and lower jaws, (6) claws, which 
as a rule are borne only by the first digit of each limb. 
Sometimes in young individuals the second digit is also clawed. 

b. The dermal exoskeleton is strongly developed, and 
is combined with endoskeletal structures derived from the ribs 
and vertebrae to form the carapace. 

The Carapace (fig. 36) consists of a number of plates 
firmly united to one another by sutures. They have a very 
definite arrangement and include : 

(a) the nuchal plate (fig. 36, 1), a wide plate forming 
the whole of the anterior margin of the carapace. It is 
succeeded by three series of plates, eight in each series, which 
together make up the main part of the carapace. Of these 
the small 

(b) neural plates 1 (fig. 36, A, 2) form the middle series. 
They are closely united with the neural arches of the under- 
lying vertebrae ; 

(c) the costal plates 1 (fig. 36, A, 3) are broad arched 
plates united to one another by long straight sutures. They 
are united at their inner extremities with the neural plates, 
but the boundaries of the two sets of plates do not regularly 
correspond. Each is united ventrally with a rib which pro- 
jects beyond it laterally for some distance ; 

1 Another view commonly held is that the neural and costal plates are 
respectively formed by the expanded neural arches and ribs. 



216 



THE VERTEBRATE SKELETON. 



(d) the marginal plates (fig. 36, 4) are twenty-three in 




FIG. 36. A, DORSAL AND B, VENTRAL VIEW OF THE CARAPACE OF A 

LOGGERHEAD TURTLE (Thalassochelys caretta), (after OWEN). 

1. nuchal plate. 6. rib. 

2. first neural plate. 7. 

3. second costal plate. 8. 

4. marginal plate. 9. 

5. pygal plate. 



thoracic vertebra, 
first vertebral shield, 
costal shield. 



THE SKELETON OF THE TURTLE. THE PLASTRON. 217 

number, eleven lying on each side, while an unpaired one lies 
in the middle line posteriorly. Many of them are marked by 
slight depressions into which the ends of the ribs tit ; 

(e) the pygal plates (fig. 36, 5) are two unpaired plates 
lying immediately posterior to the last neural. 

The sculpturing due to the epidermal shields is very 
obvious on the carapace. 

The plastron (fig. 37) consists of one unpaired ossification, 
the entoplastron, and four pairs of ossifications called re- 
spectively the epiplastra, hyoplastra, hypoplastra, and 
xiphiplastra. 

The epiplastra (fig. 37, 1) are the most anterior, they are 
expanded and united to one another in the middle line in 
front, while behind each tapers to a point which lies external 
to a process projecting forwards from the hyoplastron. They 
are homologous with the clavicles of other vertebrates. 

The entoplastron or episternum (fig. 37, 2) which is 
homologous with the interdavicle of other reptiles, is ex- 
panded at its anterior end and attached to the symphysis 
of the epiplastra, while behind it tapers to a point and ends 
freely. 

The hyoplastra are large irregular bones each closely 
united posteriorly with the corresponding hypoplastron, and 
drawn out anteriorly into a process which lies internal to that 
projecting backwards from the epiplastron. Each gives off on 
its inner surface a slender process which nearly meets its fellow, 
while the anterior half of the outer surface is drawn out into 
several diverging processes. 

The hypoplastra (fig. 37, 4) are flattened bones re- 
sembling the hyoplastra, with which they are united by long 
sutures; the posterior half of both outer and inner surfaces 
is drawn out into a number of pointed processes. 

The xiphiplastra are small flattened elongated bones 
meeting one another in the middle line posteriorly. In front 
they are notched and each interlocks with a process from the 



218 THE VERTEBRATE SKELETON. 

hypoplastron of its side. The hyoplastra, hypoplastra and 




FIG. 37. THE PLASTRON OF A GREEN TURTLE (Chelone midas). 
xf. (Camb. Mus.) 

1. epiplastron (clavicle). 4. hypoplastron. 

2. entoplastron (interclavicle). 5. xiphiplastron. 

3. hyoplastron. 

xiphiplastra are homologous with the abdominal ribs of 
Crocodiles. 

II. ENDOSKELETON. 

1. THE AXIAL SKELETON. 

The axial skeleton includes the vertebral column, the ribs, 
and the skull. 



THE SKELETOX OF THE TURTLE. THE VERTEBRAE. 219 

A. THE VERTEBRAL COLUMX AND RIBS. 

The number of vertebrae in the Green Turtle is thirty- 
eight, not a great number as compared with that in many 
reptiles, and of these eighteen are caudal. 

The vertebral column is divisible into four regions only 
cervical, thoracic, sacral, and caudal. 

THE CERVICAL VERTEBRAE. 

These are eight in number, and are chiefly remarkable for 
the great variety of articulating surfaces which their centra 
present, and for their mobility upon one another. 

The first or atlas vertebra differs much from all the others 
and consists of the following parts : 

a. the neural arch, formed of two separate ossifications 
united in the mid-dorsal line ; " 

b. the inferior arch ; 

c. the centrum, which is detached from the rest and 
forms the odontoid process of the second vertebra. 

Each half of the neural arch consists of a ventral portion, 
the pedicel, which lies more or less vertically and is united 
ventrally to the inferior arch, and of a dorsal portion, the 
lamina, which lies more or less horizontally and meets ( its 
fellow in the middle line in front, partially roofing over the 
neural canal. Each pedicel bears a facet on its anterior 
surface, which, with a corresponding one on the inferior arch, 
articulates with the occipital condyle of the skull. Three 
similar facets occur also on the posterior surface of the 
pedicel and inferior arch, and articulate with the odontoid 
process. The laminae meet one another in front, but do not 
A-faile behind they are separated by a wide triangular 
space. They bear a pair of small downwardly-directed facets, 
the postzygapophyses, for articulation with the prezyga- 
pophyses of the second vertebra. 



220 THE VERTEBRATE SKELETON. 

The inferior arch is a short irregular bone bearing two 
converging facets for articulation with the occipital condyle 
and odontoid process respectively. 

The centrum or odontoid process has a convex anterior 
surface for articulation with the neural and inferior arches, 
and a concave posterior surface by which it is united with 
the centrum of the second or axis vertebra. It bears pos- 
teriorly a small epiphysis which is really a detached portion of 
the inferior arch. 

The second or axis and following five cervical vertebrae, 
though showing distinct differences, resemble one another con- 
siderably, each having a fairly elongated centrum with a keel- 
like hypapophysis, each having also a neural arch with 
prominent articulating surfaces, the anterior of which, or 
prezygapophyses, look upwards and inwards, while the 
posterior ones, the postzygapophyses, look downwards and 
outwards. They however, as was previously mentioned, differ 
very remarkably in the character of the articulating surfaces 
of the centra. Thus the second and third vertebrae are 
convex in front and concave behind, the fourth is biconvex, 
the fifth is concave in front and convex behind. The sixth 
is concave in front and attached to the seventh by a flat 
surface behind, the seventh has a flat anterior face and two 
slightly convex facets behind. The vertebrae all have short 
blunt transverse processes and the second has a prominent 
neural spine. 

The eighth cervical vertebra is curiously modified, the 
centrum is very short, has a rather prominent hypapophysis,. 
and is convex behind, while in front it articulates with the 
preceding centrum by two concave surfaces. The neural arch 
is deeply notched in front and bears two upwardly-directed 
prezygapophyses, while behind it is very massive and is drawn 
out far beyond the centrum, bearing a pair of flat postzyga- 
pophyses. The top of the neural arch almost or quite meets 
a blunt outgrowth from the nuchal plate. 



THE SKELETON OF THE TURTLE. THE VERTEBRAE. 221 

THE THORACIC VERTEBRAE. 

These are ten in number and are all firmly united with 
the ribs and elements forming the carapace. 

The first thoracic vertebra differs from the others, the 
centrum is short and has a concave anterior surface articu- 
lating with the centrum of the last cervical vertebra, and a 
pair of prezygapophyses borne on long outgrowths. The 
neural spine arises only from the anterior half of the centrum, 
and is not fused to the carapace. Arising laterally from the 
anterior part of the centrum are a small pair of ribs each of 
which is connected with a process arising from the rib of the 
succeeding vertebra. 

The next seven thoracic vertebrae are all very similar, 
each has a long cylindrical centrum, expanded at the ends, 
and firmly united to the preceding and succeeding vertebrae. 
The neural arches are flattened and expanded dorsally, "and 
are united to one another and to the overlying neural 
plates ; each arises only from the anterior half of its respective 
centrum, and overlaps the centrum of the vertebra in front of 
it. Between the base of the neural arch and its successor is a 
small foramen for the exit of the spinal nerve. There are no_ 
transverse processes or zygapophyses. 

To each thoracic vertebra from the second to ninth in- 
clusive, there corresponds a pair of ribs (fig. 36, 6) of a rather 
special character. Each is suturally united with the anterior 
half of the edge of its own vertebra, and overlaps on to the 
posterior half of the edge of the next preceding vertebra. 
The ribs are much flattened, and each is fused with the cor- 
responding costal plate, beyond which it projects to fit into 
a pit in one of the marginal plates. 

The tenth thoracic vertebra is smaller than the others, and 
its neural arch does not overlap the preceding vertebra, it 
bears a pair of small ribs which are without costal plates, but 
meet those of the ninth vertebra. 

There are no lumbar vertebrae. 



222 THE VERTEBRATE SKELETON. 

THE SACRAL VERTEBRAE. 

The sacral vertebrae are two in number, they are short 
and wide, their centra are ankylosed together, and their neural 
arches are not united to the carapace. 

The first has the anterior face of the centrum concave and 
the posterior flat, while both faces of the second are flat. 
Each bears a pair of short ribs which meet the ilia, but are 
not completely ankylosed either with them or the centra. 

THE CAUDAL VERTEBRAE. 

The caudal vertebrae are eighteen in number. The 
centrum of the first is flat in front and is ankylosed to 
the second sacral ; behind it is convex. The others are all 
very similar to one another, and decrease gradually in size 
wnen followed back. Each has a moderately long centrum, 
concave in front and convex behind, both terminations being 
formed by epiphyses. The neural arch arises only from the 
anterior half of the vertebra ; it bears a blunt truncated 
neural spine and prominent pre- and post-zygapophyses. The 
first seven caudal vertebrae bear short ribs attached to their 
lateral margins, the similar outgrowths on the succeeding ver- 
tebrae do not ossify from distinct centres, and are transverse 
processes rather than ribs. 

B. THE SKULL. 

The skull of the Turtle is divisible into the following three 
parts. : 

(1) the cranium ; 

(2) the lower jaw or mandible ; 

(3) the hyoid. 

(1) THE CRANIUM. 

The cranium is a very compact bony box, containing ;t 
cavity in which the brain lies, and which is a direct continua- 
tion of the neural canal of the vertebrae. 



THE SKELETON OF THE TURTLE. THE SKULL. 223 




17 



FIG. 38. THE SKCLL OF THE GHEEX TURTLE (Chelone midas). x 4. 

A, POSTERIOR HALF, B, ANTERIOR HALF. (Brit. MuS.) 

1. parietal. 13. angular. 

2. squamosal. 14. supra-angular. 

3. quadrate. 15. premaxilla. 

4. basisphenoid. 16. maxilla. 

5. basi-occipital. 17. jugal. 

6. quadratojugal. 18. postfrontal. 

7. opisthotic. 19. vomer. 

8. exoccipital. 20. prefrontal. 

9. foramen magnum. 21. frontal. 

10. splenial. 22. external auditory meatus 

11. articular. leading into tympanic 

12. deutary. cavity. 



224 THE VERTEBRATE SKELETON. 

Like those of the skull as a whole its component bones may 
be subdivided into three sets : 

1 . those forming the brain-case or cranium proper ; 

2. those developed in connection with the special sense 
organs ; 

3. those forming the upper jaw and suspensorial appa- 
ratus. 

Both cartilage and membrane bones take part in the forma- 
tion of the skull, and a considerable amount of cartilage 
remains unossified, especially in the ethmoidal and sphenoidal 
regions. 

1. The CRANIUM PROPER OR BRAIN-CASE. 

The cartilage and membrane bones of the brain-case when 
taken together can be seen to be more or less arranged in 
three rings or segments, called respectively the occipital, 
parietal, and frontal segments. 

The occipital segment is the most posterior of these, and 
consists of four cartilage bones, the basi-occipital, the two 
exoccipitals and the supra-occipital ; these bound the 
foramen magnum. 

The basi-occipital (figs. 38 and 39, 5) lies ventral to the 
foramen magnum and only bounds a very small part of it ; it 
forms one-third of the occipital condyle by which the skull 
articulates with the atlas vertebra. It unites dorsally with 
the exoccipitals and anteriorly with the basisphenoid. 

The exoccipitals are rather small bones, which form the 
sides and the greater part of the floor of the foramen magnum, 
and two-thirds of the occipital condyle. Laterally each is 
united with the pterygoid and opisthotic of its side. At the 
sides of the occipital condyle each exoccipital is pierced by 
a pair of foramina, the more dorsal and posterior of which 
transmits the hypoglossal nerve. 

The supra-occipital (tig. 39, 14) is a larger bone than the 
others of the occipital segment. It forms the upper border 



THE SKELETON OF THE TURTLE. THE CRANIUM. 225 

of the foramen magnum and is drawn out dorsally into a large 
crest which extends back far beyond the occipital condyle. 
In the adult the supra-occipital is completely ankylosed with 
the epi-otics. 

The Parietal segment. 

The ventral portion of the parietal segment is formed by 
the basisphenoid (figs. 38 and 39, 4) which lies immediately 
in front of the basi-occipital. A triangular portion of it is 
seen in a ventral view of the skull, but it is quickly over- 
lapped by the pterygoids. It gives off dorsally a pair of 
short processes which meet the pro-otics. 

The alisphenoidai region is unossified and the only other 
constituents of the parietal segment are the parietal* (fig. 39, 1). 
These are large bones which, after roofing over the cranial 
cavity, extend upwards and become expanded into a pair of 
broad plates which unite with the squamosal and bones of the 
frontal segment to form a wide, solid, false roof to the skull. 
Each also sends ventralwards a plate which meets an up- 
growth from the pterygoid and acts as an alisphenoid. 

The Frontal segment. 

Of the frontal segment the basal or presphenoidal and 
lateral or orbitosphenoidal portions do not become ossified, 
the dorsal portion however includes three pairs of membrane 
bones, the frontal s, prefrontals and postfrontals. 

Tb&Jrontalg are a pair of small bones lying immediately in 
front of the parietals, and in front of them are the prefrontals 
(tigs. 38 and 39, 20), a pair of similar but still smaller bones, 
which are produced ventrally to meet the vomer and palatines. 
They form also the dorsal boundary of the anterior nares. 
The postfrontals (figs. 38 and 39, 18) are larger bones, united 
dorsally to the frontals and parietals, posteriorly to the squa- 
mosals, and ventrally to the jugals and quadra tojugals. All 
three pairs of frontal bones, especially the postfrontals, take 
part in the bounding of the orbits. 

R. 15 



226 



THE VERTEBRATE SKELETON. 



B^ 

x+* 

R"8 

* <n 

X 
X * 

HH 



ot- 



S ,1-fPS 

-i s S g 3 F .9 

lllllpf 

oc os o i-I **" 

iH i-l <M (M 




THE SKELETON OF THE TURTLE. SENSE CAPSULES. 227 

~2. THE SEXSE CAPSULES. 

Skeletal structures occur in connection with each of the 
three special sense organs of hearing, sight, and smell. 

The Auditory capsules. 

The auditory or periotic capsule of the turtle is rather 
large and its walls are well ossified, epi-otic, pro-otic and 
opisthotic bones being present. 

The epi-otic (fig. 39, 13) is the more dorsal of the three 
bones, and in the adult is completely ankylosed with the supra- 
occipital. 

The opisthotic (fig. 39, 8) is the ventral posterior element. 
On its inner side it is united to the supra-occipital above, 
and to the exoccipital below ; it sometimes becomes com- 
pletely fused with the exoccipital. In front it meets the 
pro-otic, and on its outer side the squamosal and quadrate. 
Its anterior portion is hollowed out by the cavity in which 
the auditory organ lies, it gives off also a process which is 
separated from the exoccipital by an oval foramen through 
which the glossopharyngeal, pneumogastric, and spinal acces- 
sory nerves leave the cranial cavity. 

The pro-otic is the anterior element: it meets the supra- 
occipital and opisthotic posteriorly, while anteriorly it is 
separated from the alisphenoidal plate of the parietal and 
pterygoid by a large oval foramen through which the maxillary 
and mandibular branches of the trigeminal nerve pass out 
(fig. 39, V 1 fc 2). It is hollowed out posteriorly by the cavity 
which the auditory organ lies, and its inner wall as seen in 
longitudinal section is pierced by a foramen through which the 
external carotid artery and facial nerve leave the cranial cavity, 
the nerve finally leaving the skull through a small oval 
foramen on the anterior face of the pro-otic near its junction 
with the quadrate. 

Between the pro-otic and opisthotic as seen in a longi- 
tudinal section of the skull is a large opening constricted in the 

152 



228 THE VERTEBRATE SKELETON. 

middle. This is the internal auditory meatus (fig. 3 9, VIII.). 
Through it the auditory nerve leaves the cranial cavity and 
enters the ear. The ramus vestibularis leaves through the dorsal 
part of the hole, the ramus cochlearis through the ventral. 

The cavity of the auditory or periotic capsule communi- 
cates with the exterior by a fairly large hole, the fenestra 
ovalis, which lies between the opisthotic and pro-otic, and 
opens into a deep depression, the tympanic cavity, which 
is seen in a posterior view of the skull lying just external to 
the exoccipital. The cavity communicates with the exterior by 
a large opening, the external auditory meatus (fig. 38, 22). 

Several other openings are seen in the tympanic cavity; 
through one at the extreme posterior end the pneumogastric 
and spinal accessory nerves leave the skull, and through 
another, a little further forwards, the glossopharyngeal. 

The auditory ossicles consist of a long bony columella, 
whose inner end fits into the fenestra ovalis, while the outer 
end is attached to a small cartilaginous plate, the extra- 
columella, which is united to the tympanum. 

The Optic capsules. 

The skeletal structures developed in connection with the 
optic capsule do not become united to the skull. They con- 
sist of : 

() the sclerotic, a cartilaginous sheath investing the eye 
and bearing 

(6) a ring of ten small bony scales. 

There is no lachrymal bone. 

The Olfactory or Nasal capsules. 

The basicranial axis in front of the basisphenoid remains 
cartilaginous, neither presphenoid nor mesethmoid bones are 
developed, and the orbits in a dry skull communicate by a 
wide space through which the second, third, fourth, and sixth 
cranial nerves pass out. Separate nasal bones also do not 
occur, the large prefrontals extending over the area usually 
occupied by both nasals and lachrymals. 



THE SKELETON OF THE TURTLE. THE UPPER JAW. 229 

The only bone developed in connection with the nasal 
capsules is the vomer (fig. 39, 19), an unpaired bone lying 
ventral to the mesethmoid cartilage, and in contact laterally 
with the maxillae, preinaxillae and palatines. 

3. THE UPPER JAW AND SUSPEXSORIAL APPARATUS. 

A number of pairs of bones are developed in connection 
with the upper jaw and suspensorial apparatus, one pair, the 
quadrates, being cartilage bones, while the rest are all mem- 
brane bones. 

The squariwsals (fig. 38, 2) are large bones which, lying 
external to the auditory bones, extend dorsalwards to meet 
the parietals and postfrontals, and form a large part of the 
false roof of the skull. They are united ventrally with the 
quadrates and quadra tojugals. 

Each quadrate (fig. 38, 3) forms the outer boundary of 
the tympanic cavity, and is firmly united on its inner side with 
the opisthotic, exoccipital, and pterygoid. Dorsally it is fixed 
to the squamosal and anteriorly to the quadratojugal. Its 
outer surface is marked by a deep recess, and it ends below 
in a strong condyle with which the mandible articulates. In 
front of the quadrates are a pair of thin plate-like bones, the 
qn.adratojugals which are united in front to the jugals or malars. 

The jitgals (tig. 38, 17) are also thin plate-like bones, and 
form part of the posterior boundary of the orbit. They are 
attached dorsally to the postfrontals, and anteriorly to the 
maxillae, while each also sends inwards a horizontal process 
which meets the pterygoid and palatine. 

The maxillae (figs. 38 and 39, 16) are a pair of large ver- 
tically-placed bones, each drawn out ventrally into a straight, 
sharp, cutting edge. They form the lateral boundaries of the 
anterior nares, and each sends dorsalwards a process which 
meets the post-frontal. Each also sends inwards a horizontal 
palatine process, which meets the palatine and vomer, and 
also forms much of the floor of the narial passage. 



230 THE VERTEBRATE SKELETON. 

The premaxillae (figs. 38 and 39, 15) are a pair of very 
small bones forming the floor of the anterior narial opening, 
they are wedged in between the two maxillae, and send back 
processes which meet the vomer and palatines. 

The palatines (fig. 39, 10) are a pair of small bones firmly 
united with the pterygoids behind, with the maxillae and jugals 
externally, and with the vomer in the middle line. Each also 
gives off a palatine plate which unites with the expanded lower 
edge of the vomer, and forms the ventral boundary of the pos- 
terior nares. Anteriorly the palatines form the posterior bound- 
ary of a large foramen through which the ophthalmic branches 
of the fifth and seventh nerves pass to the olfactory organs. 

The pterygoids (fig. 39, 9) are a pair of large bones which 
unite with one another by a long median suture. They are 
united also with the palatines in front, and with the quadrate, 
basisphenoid, basi-occipital, and exoccipitals behind. Each 
also sends dorsalwards a short alisphenoid plate which 
meets that from the parietal. 

Piercing the posterior end of the pterygoid is the prominent 
opening of the carotid canal; a bristle passed into this hole 
emerges through a foramen lying between the pro-otic and the 
alisphenoid process of the pterygoid. 

(2) THE LOWER JAW OR MANDIBLE. 

The mandible consists of one unpaired bone, formed by 
the fusion of the two dentaries, and five pairs of bones, called 
respectively the articular, angular, supra-angular, splenial 
and coronoicl. 

The fused dentaries (fig. 38, 12) form by far the largest of 
the bones ; they constitute the flattened anterior part of the 
mandible, and extend back below the other bones almost to 
the end of the jaw. 

The coronoid is the most anterior of the paired bones, it 
forms a prominent process to which the muscles for closing 
the jaw are attached. 



THE SKELETON OF THE TURTLE. THE HYOID. 231 

The articular (tig. 38, 11) is expanded, and with the supra- 
angidar forms the concave articulating surface for the quadrate. 

The splenial (fig. 38, 10) is a thin plate applied to the inner 
surface of the posterior part of the mandible. 

The angular (fig. 38, 13) is a slender plate of bone lying 
below the supra-angular and splenial. 

(3) THE HYOID. 

The hyoid apparatus is well developed, parts of the first two 
branchial arches being found, as well as of the hyoid proper. 
It consists of a more or less oblong flattened basilingual 
plate or body of the hyoid which represents the fused 
ventral ends of the hyoid and branchial arches of the embryo, 
and is drawn out into a point anteriorly. The greater part is 
formed of unossitied cartilage, but at the posterior end it is 
bilobed, and a pair of ossified tracts occur. To its sides are 
attached three pairs of structures, which are portions of the 
hyoid and first and second branchial arches respectively. 

The free part of the hyoid consists of a small piece of 
cartilage attached to the anterior part of the basilingual plate 
at its widest portion (fig. 53, 2). 

The anterior cornu or free part of the first branchial 
arch is much the largest of the three structures. Its proximal 
portion adjoining the basilingual plate is cartilaginous, as is 
its distal end ; the main part is however ossified. 

The posterior cornu or free part of the second branchial 
arch (fig. 53, 4) consists of a short flattened cartilaginous bar 
arising from the bilobed posterior end of the basilingual plate. 

The hyoid apparatus has no skeletal connection with the 
rest of the skull. 

2. THE APPENDICULAR SKELETON. 

This includes the skeleton of the two pairs of limbs and 
their girdles. 

THE PECTORAL GIRDLE. 

The pectoral girdle has an anomalous position, being 



232 THE VERTEBRATE SKELETON. 

situated internal or ventral to the ribs. It consists of three 
bones, a dorsal bone, the scapula, an anterior ventral bone, 
the precoracoid, and a posterior ventral bone, the coracoid. 

The scapula is a small somewhat rod-shaped bone form- 
ing about two-thirds of the glenoid cavity. At its proximal 
end it is closely united with the precoracoid, the two bones 
ossifying continuously. It tapers away distally, and is directed 
dorsalwards towards the carapace. 

The precoracoid forms an angle of about 130 with the 
scapula, with which it is completely fused at its proximal end. 
Its distal end is somewhat expanded and flattened, and is 
terminated by a fibrocartilaginous epiprecoracoid which 
meets its fellow. It takes no part in the formation of the 
glenoid cavity. 

The coracoid is a large flattened blade-shaped bone form- 
ing about one-third of the glenoid cavity. It does not meet 
its fellow in a ventral symphysis, and is terminated by a carti- 
laginous epicoracoid. The glenoid articulating surfaces of 
both scapula and coracoid are lined by a thick pad of car- 
tilage. 

THE ANTERIOR LIMB. 

This is divisible into three portions, the upper arm, fore- 
arm and manus. 

The upper arm contains a single bone, the humerus. 

The humerus (tig. 40, A, 1) is a stout, nearly straight, some- 
what flattened bone widely expanded at both ends. At the 
proximal end is the large hemispherical head, which articulates 
with the glenoid cavity. Behind the head the bone is drawn 
out into another large rounded process. Below the head tin- 
shaft bears a small outgrowth which is continuous with a 
larger one on the flexor surface (see p. 29). The bone is 
terminated distally by the trochlea, consisting of three 
partially distinct convex surfaces which articulate with the 
bones of the fore-arm. 



THE SKELETON OF THE TURTLE. ANTERIOR LIMB. 233 

The fore- arm includes two bones, the radius and ulna; 
both these are small bones, and are immovably fixed to one 
another proximally and distally. 

The radius or pre-axial bone is the larger of the two, and 
is a rod-like bone terminated at either end by an epiphysis. 
It articulates at its proximal end with the humerus, and at 
its distal end with the radiale or scaphoid bone of the carpus. 

The ulna (fig. 40, A, 3) or post-axial bone is shorter than 
the radius, and more expanded at its proximal end, where it 
articulates with the humerus. It articulates distally with the 
intermedium (lunar) and the ulnare (cuneiform) bones of the 
carpus. All three bones of the arm have their terminations 
formed by epiphyses which ossify from centres distinct from 
those forming the shafts. 

The Manus consists of the carpus or wrist and the hand 
which includes the metacarpals and phalanges. 

The carpus consists of a series of ten small bones, one of 
which, the pisiform (fig. 40, A, 10), differs from the others in 
being merely an ossification in the tendon of a muscle. The 
remaining nine bones are arranged in a proximal row of three, 
the ulnare (fig. 40, A, 6), intermedium, and radiale, and a 
distal row of five (carpalia 1 5), each of which supports one 
of the metacarpals. A ninth bone, the centrale (fig. 40, A, 7), 
is wedged in between the two rows. The ulnare, intermedium 
and pisiform are comparatively large flattened bones, the others 
are small and cubical. 

The hand. This is composed of five digits, each of which 
consists of a metacarpal and of a varying number of phalanges. 

The metacarpals. The first metacarpal (fig. 40, A, 11) 
i^ a short flattened bone, the others are all elongated and 
cylindrical, and are terminated proximally by slightly concave 
surfaces, and distally by slightly convex ones. 

The phalanges. The first and fifth digits both have two 
phalanges, the second, third, and fourth have each three. The 
distal phalanx of the first digit is stout and curved, and bears 



234 



THE VERTEBRATE SKELETON. 




FIG. 40. A. ANTERIOR LIMB OF A YOUNG HAWKSBILL TURTLE (Chelone 
imbricata) x | (Brit. Mus.). B. POSTERIOR LIMB OF A LARGE GREEN 
TURTLE (Chelone midas) x \ (Camb. Mus.). 



1. 


humerus. 


012. 


femur. 


2. 


radius (almost hidden by the 


13. 


tibia. 




ulna). 


14. 


fibula. 


3. 


ulna. 


15. 


tibiale intermedium and ceu- 


4. 


radiale. 




trale fused. 


5. 


intermedium. 


16. 


fibulare. 


6. 


ulnare. 


17. 


tar sale 1. 


7. 


centrale. 


18. 


tarsale 2. 


8. 


carpale I. 


19. 


tarsalia 4 and 5 fused. 


9. 


carpale IV. 


20. 


first metatarsal 


10. 


pisiform. 


21. 


fifth metatarsal. 


11. 


first metacarpal. 


I, 


II, III, IV, V, digits. 



THE SKELETON OF THE TURTLE. PELVIC GIRDLE. 235 

a horny claw ; those of the other digits are flattened and more 
or less pointed. 

THE PELVIC GIRDLE. 

The pelvic girdle consists of three bones ; a dorsal bone, 
the ilium, an anterior ventral bone, the pubis, and a pos- 
terior ventral bone, the ischium. All three bones contribute 
largely to the formation of the acetabulum, with which the 
head of the femur articulates. 

The ilium is a small slightly curved bone, which unites 
ventrally with the pubis and ischium, and extends dorsalwards 
and backwards to meet the distal ends of the sacral ribs. 

The pubis is the largest bone of the three ; its distal 
end forms a wide bilobed plate, the inner lobe meeting its 
fellow in a median symphysis, while the other lobe or lateral 
process extends outwards. Attached to the symphysis in front 
is a cartilaginous epipubis, while behind, the two pubes are 
terminated by a wide rounded cartilaginous area. 

The ischium, the smallest bone of the three, is flattened 
and like the pubis -meets its fellow in a median symphysis. 
A narrow band of cartilage connects the symphysis pubis with 
the symphysis ischii, and separates the two obturator fora- 
mina from one another. 

THE POSTERIOR LIMB. 

This is divisible into three portions, the thigh, the cms or 
shin, and the pes. 

The thigh includes a single bone, the femur. 

The femur (fig. 40, B, 12) is a short thick bone, with a 
prominent rounded head articulating with the acetabulum. 
Behind this head is a deep pit, beyond which is a roughened 
area corresponding with the great trochanter of mammals. 
The distal end is expanded and somewhat convex. 

The bones of the cms or shin are the tibia and 
fibula. These are both straight rod-like bones with expanded 



236 THE VERTEBRATE SKELETON. 

terminations which closely approach one another, while else- 
where the bones diverge considerably. 

The terminations of all three of the leg bones are formed 
by epiphyses. 

The Pes consists of the tarsus or ankle, and the foot, 
which is made up of five digits. 

The tarsus. The tarsal bones of the Turtle do not retain 
their primitive arrangement to such an extent as do the 
carpals. They are arranged in a proximal row of two and a 
distal row of four. Of the bones in the proximal row the 
postaxial one is much the smaller and is the fibulare ; the 
larger pre-axial one (fig. 40, B, 15) represents the tibiale, 
intermedium, and centrale fused, and articulates with both 
tibia and fibula. The first three distal tarsalia are all small 
bones and are very similar in size, and each articulates regu- 
larly with the corresponding metatarsal. The fourth bone 
(fig. 40, B, 19) is much larger, and represents tarsalia 4 and 5 
fused. The first two distal tarsalia articulate with the pre- 
axial tarsal of the proximal row, the third only with its neigh- 
bours the second, and the fused fourth and fifth. The latter 
articulates with both bones of the proximal row. 

Each digit consists of a metatarsal and of a varying num- 
ber of phalanges. 

The metatarsals. The first metatarsal (fig. 40, B, 20) 
is broad and flattened, the second, third and fourth, are all 
elongated bones with nearly flat terminations formed by small 
epiphyses. The fifth is large and flattened, and the articular 
surface for the phalanx is situated somewhat laterally. 

The phalanges. The first digit has two phalanges and is 
the stoutest of them all ; its distal phalanx is sheathed in a 
large horny claw. The other digits, of which the third is the 
longest, have each three phalanges. The distal phalanges of 
the second and third digits are flattened and pointed and bear 
small horny claws. 



CHAPTER XV. 
THE SKELETON OF THE CROCODILE. 

THE species chosen for description is C. paltistris, a form 
occurring throughout the Oriental region, but the description 
would apply almost equally well to any of the other species of 
the genus Crocodihis, and with comparatively unimportant 
modifications to any of the living Crocodilia. 

I. EXOSKELETON. 

The exoskeleton of the Crocodile is strongly developed and 
includes elements of both epidermal and dermal origin. 

. The epidermal exoskeleton is formed of a number 
of horny scales or plates of variable size covering the whole 
surface of the body. Those covering the dorsal and ventral 
surfaces are oblong in shape, and are arranged in regular rows 
running transversely across the body. The scales covering 
the limbs and head are mostly smaller and less regularly 
arranged, and are frequently raised into a more or less obvious 
keel. Those covering the dorsal surface of the tail are very 
prominently keeled. 

The epidermal exoskeleton also includes the horny claws 
borne by the first three digits of both manus and pes. 

b. The dermal exoskeleton. This has the form of 
bony scutes which underlie the epidermal scales along the 
dorsal surface of the trunk and anterior part of the tail 



238 THE VERTEBRATE SKELETON. 

Except in very young individuals the epidermal scales are 
rubbed off from these scutes, which consequently come to pro- 
ject freely on the surface of the body. Each scute is a nearly 
square bony plate, deeply pitted or sculptured, and marked by 
a strong ridge on its dorsal surface, while its ventral surface 
is smooth. Contiguous scutes are united to one another by 
interlocking sutures. 

The* scutes are arranged in two distinct areas, viz. (1) a 
small anterior nuchal shield which lies just behind the head 
and is formed of six large scutes more or less firmly united 
together, and (2) a larger posterior dorsal shield covering the 
whole of the back and anterior part of the tail, and formed 
of smaller scutes, which are arranged in regular transverse 
rows, and progressively diminish in size when followed back. 

The teeth are exoskeletal structures, partly of dermal, 
partly of epidermal origin. They lie along the margins of 
the jaws and are confined to the premaxillae, maxillae and 
dentaries. They are simple conical structures, without roots ; 
each is in the adult placed in a separate socket, and is replaced 
by another which as it grows comes to occupy the pulp cavity 
of its predecessor. In the young animal the teeth are not 
placed in separate sockets but in a continuous groove. Tin's 
feature is met with also in the Ichthyosauria. The groove 
gradually becomes converted into a series of sockets by the 
ingrowth of transverse bars of bone. The anterior teeth are 
sharply pointed and slightly recurved, the posterior ones are 
more blunt. 

The upper jaw bears about nineteen pairs of teeth, the 
lower jaw about fifteen pairs. The largest tooth in the upper 
jaw is the tenth, and in the lower jaw the fourth. 

The three living families of Crocodilia, the Crocodiles, 
Alligators and Garials, can be readily distinguished by the 
characters of the first and fourth lower teeth. In Alligators 
both first and fourth lower teeth bite into pits in the upper 
jaw; in Garials they both bite into notches or grooves in 



SKELETON OF THE CROCODILE. VERTEBRAL COLUMN. 239 



the upper jaw. In Crocodiles the first tooth bites into a pit, 
the fourth into a notch in the upper jaw. 

II. EXDOSKELETOK 

1. THE AXIAL SKELETON. 

This includes the vertebral column, the skull, and the ribs 
and sternum. 

A. THE VERTEBRAL COLUMN. 

The vertebral column is very long, consisting of some sixty 
vertebrae. It can be divided into the usual five regions, the 
cervical, thoracic, lumbar, sacral, and caudal regions. 




10 -^ 



FIG. 41. 



FlBST FOCE CERVICAL VEKTEBBAE OF A CROCODILE (C. 

(Partly after vox ZITTEL.) 

pro-atlas. 7. tubercular portion of fourth 

lateral portion of atlas, 
odontoid process. 8. 

ventral portion of atlas. 9. 

neural spine of axis. 10. 

postzygapophysis of fourth 
vertebra. 



cervical rib. 
first cervical rib. 
second cervical rib. 
convex posterior surface of 

centrum of fourth vertebra. 



THE CERVICAL VERTEBRAE. 

Counting as cervical all those vertebrae which are anterior 
to the first one whose ribs meet the sternum, there are nine 
cervical vertebrae, all of which bear ribs. 

As a type of the cervical vertebrae the fifth may be taken. 



240 THE VERTEBRATE SKELETON. 

It has a short cylindrical centrum deeply concave in front 
and convex behind. From the anterior part of the ventral 
surface of the centrum arises a short hypapophysis, and 
on each side is a facet with which the lower limb (capi- 
tulum) of the cervical rib articulates. The neural arch is 
strongly developed and drawn out dorsally into a long neural 
spine, in front of which are a pair of upstanding processes 
bearing the prominent upwardly and inwardly directed pre- 
zygapophyses. At the sides and slightly behind the neural 
spine are a corresponding pair of processes bearing the post- 
zygapophyses, which look downwards and outwards. At 
the point where it joins the centrum the neural arch is drawn 
out into a short blunt transverse process with which the 
upper limb (tuberculum) of the cervical rib articulates. The 
sides of the neural arch are slightly notched behind for the exit 
of the spinal nerves. 

The first or atlas vertebra differs much from any of the 
others, and consists of four quite detached portions, a ventral 
arch, with two lateral portions and one dorsal. The ventral 
arch (fig. 41, 4) is flat below and slightly concave in front, 
forming together with two flattened surfaces on the lateral 
portions a large articulating surface for the occipital condyle 
of the skull. Its posterior face is bevelled off and forms with 
a second pair of facets on the lateral portions a surface with 
which the odontoid process of the second vertebra articulates. 
The postero-lateral surfaces of the ventral arch also bear a pair of 
little facets with which the cervical ribs articulate. The lateral 
portions are somewhat flattened and expanded, and bear in ad- 
dition to those previously mentioned a pair of small downwardly 
directed facets, the postzygapophyses, which articulate with the 
prezygapophyses of the second vertebra. The dorsal portion 
(fig. 41, 1) is somewhat triangular in shape, and overhangs the 
occipital condyle. It is often regarded as the neural arch of a 
vertebra in front of the atlas and is called the pro-atlas ; but 
as it is a membrane bone it is not properly a vertebral element. 



SKELETON OF THE CROCODILE. VERTEBRAL COLUMN. 241 

The second or axis vertebra also differs a good deal from 
the other cervicals. The centrum is massive, and is terminated 
in front by a very large slightly concave articulating surface 
formed by the odontoid process (fig. 41, 3) which is united 
with the centrum by suture only, and is really the detached 
centrum of the first vertebra. The cervical rib (fig. 41, 9) 
articulates with two little irregularities on the odontoid pro- 
cess. The posterior surface of the centrum is convex. The 
neural arch is strongly developed and terminated dorsally 
by a long neural spine (fig. 41, 5), its sides are notched, 
slightly in front and more prominently behind for the exit of 
the spinal nerves. It is drawn out in front into two little 
processes bearing a pair of upwardly and outwardly directed 
prezygapophyses, while the postzygapophyses are similar to 
those of the other cervical vertebrae. 

The last two cervical vertebrae resemble the succeeding 
thoracic vertebrae, in the increased length of the transverse 
processes, and the shifting dorsalwards of the facet with which 
the capitulum of the rib articulates. 

THE THORACIC VERTEBRAE- 

The thoracic vertebrae commence with the first of those 
that tears ribs reaching the sternum. They are ten in 
number, and the first eight are directly connected with the 
sternum by ribs. 

The third of them may be taken as a type. It has a 
thick cylindrical centrum, concave in front and convex behind, 
there is a slight hypapophysis, and the centrum is suturally 
united with a strong neural arch enclosing a narrow neural 
canal. The neural arch is drawn out dorsally into a wide 
truncated neural spine, and laterally into two prominent 
transverse processes, with the ends of which the tubercula of 
the ribs articulate, while the capitulum articulates in each case 
with a step-like facet (tig. 42, A, 3) on the anterior face of the 
transverse process. The prezygapophyses (fig. 42, A, 2) are 
R. 16 



242 



THE VERTEBRATE SKELETON. 



borne on outgrowths from the bases of the transverse pro- 
cesses, and the postzygapophyses on outgrowths at the base of 
the neural spine. 

The thoracic vertebrae behind the third have no hypa- 
pophyses, and the capitular facets gradually come to be placed 
nearer and nearer the ends of the transverse processes, at the 
same time becoming less prominent ; otherwise these vertebrae 
are just like the third. 

A B 




6 

FIG. 42. ANTEKIOR VIEW OF A, A LATE THORACIC AND B, THE FIRST SACRAI, 

VERTEBRA OF A YOUNG CROCODILE (C. palustris). X ^. 



1. neural spine. 4. 

2. process bearing prezygapo- 5. 

physis. 

3. facet for articulation with the 6. 

capitulum of the rib. 



sacral rib. 

surface which is united with 
the ilium. 

concave anterior face of cen- 
trum. 



In the first and second thoracic vertebrae the capitulum of 
the rib articulates, not with a facet on the transverse process, 
but with a little elevation borne at the line of junction of the 
centrum and neural arch. 

THE LUMBAR VERTEBRAE. 

These are five in number, and are precisely like the 
posterior thoracic vertebrae, except in the fact that the 
transverse processes have no facets for the articulation of ribs. 



SKELETON OF THE CROCODILE. VERTEBRAL COLUMN. 243 

THE SACRAL VERTEBRAE. 

These are two in number, and while the centrum of the 
first is concave in front (fig. 42, B, 6) and nearly flat behind, 
that of the second is flat in front and concave behind. Each 
has a pair of strong ribs (tig. 42, B, 4) firmly ankylosed in the 
adult with a wide surface furnished partly by the centrum, 
partly by the neural arch. The distal ends of these ribs are 
united with the ilia. The character of the neural spines and 
zygapophyses is the same as in the thoracic vertebrae. 

THE CAUDAL VERTEBRAE. 

These are very numerous, about thirty-four in number. 
The first differs from all the other vertebrae of the body in 
having a biconvex centrum. The succeeding ones are procoe- 
lous and are very much like the posterior thoracic and lumbar 
vertebrae, having high neural spines and prominent straight 
transverse processes. They differ however in having the 
neural spines less strongly truncated above, and the transverse 
processes arise from the centra and not from the neural 
arches. When followed furtKer back the centra and neural 
spines gradually lengthen while the transverse processes be- 
come reduced, and after the twelfth vertebra disappear. 
Further back still the neural spines and zygapophyses 
gradually become reduced and disappear, as finally the neural 
arch does also, so that the last few vertebrae consist simply of 
cylindrical centra. 

Each caudal vertebra, except the first and the last eleven 
or so, has a V-shaped chevron bone attached to the postero- 
ventral edge of its centrum. The anterior ones are the largest 
and they gradually decrease in size till they disappear. 

B. THE SKULL 1 . 

The skull of the Crocodile is a massive depressed structure 

1 Free use has been made of L. C. Miall's Studies in Comparative 
Anatomy, i., The Skull in Crocodilia, London, 1878. See also W. K. 
Parker, Tr. Z. S., vol. xi. 1885, p. 263. 

162 



244 THE VERTEBRATE SKELETON. 

presenting a number of striking characteristics, some of the 
more important of which are : 

1. All the bones except the mandible, hyoid, and columella 
are firmly united by, interlocking sutures. In spite of this, 
however, growth of the whole skull and of the component 
bones goes on continuously throughout life, this growth being 
especially marked in the case of the facial as opposed to the 
cranial part of the skull. 

2. All the bones appearing on the dorsal surface are 
remarkable for their curious roughened and pitted character ; 
this feature is prominent also in many Labyrinthodonts. 

3. The size of the jaws and teeth is very great. 

4. The mandibular condyle is carried back to some dis- 
tance behind the occipital condyle. 

5. The occipital plane (see p. 386) of the skull is vertical. 

6. The length of the secondary palate is remarkably great, 
and the vomer takes no part in its formation. 

7. The posterior nares are placed very far back, the nasal 
passages being as in mammals separated from the mouth by 
the long secondary palate. 

8. There is a complicated system of Eustachian passages 
communicating at one end with the tympanic cavity and at 
the other end with the mouth cavity. 

9. The interorbital septum is mainty cartilaginous, the 
presphenoidal and orbitosphenoidal regions remaining un- 
ossified. 

The skull is divisible into three parts : 

(1) the cranium, (2) the lower jaw, (3) the hyoid. 

The cranium may again for purposes of description be 
divided into : 

1. the cranium proper or brain case ; 

2. the bones connected with the several special sense 
organs ; 

3. the bones of the upper jaw, and suspensorial apparatus. 



SKELETON OF THE CROCODILE. THE SKULL. 24-5 



1. THE CRANIUM PROPER OR BRAIX CASE. 

The cartilage and membrane bones of the cranium proper 

A B 



21 



3 




FIG. 43. PALATAL ASPECT A, OF THE CRANIUM, B, OF THE MANDIBLE OF 
AN ALLIGATOR (Caiman latirostris). x |. (Brit. Mus.) 



1. premaxilla. 

'2. maxilla. 

3. palatine. 

4. pterygoid. 

5. posterior nares. 

6. transpalatine. 

7. posterior palatine vacuity. 

8. anterior palatine vacuity. 

9. basi-occipital. 

10. opening of median Eusta- 

cbian canal. 

11. jugal. 



12. quadratojugal. 

13. quadrate. 

14. dentary. 

15. splenial. 

16. coronoid. 

17. supra-angular. 

18. angular. 

19. articular. 

20. lateral temporal fossa. 

21. openings of vascular canals 

leading into alveolar sinus. 



246 THE VERTEBRATE SKELETON. 

when taken together can in most vertebrates be seen to be 
more or less arranged in three rings or segments called respec- 
tively the occipital, parietal and frontal segments ; in the 
Crocodile however only the occipital and parietal segments 
are clearly seen. 

The occipital segment consists of four cartilage bones, 
three of which together surround the foramen magnum. 

The most ventral of these, the basi-occipital (figs. 43 
and 45, 9), forms the single convex occipital condyle for 
articulation with the atlas, bounds the base of the foramen 
magnum, and is continuous laterally with two larger bones, 
the exoccipitals (fig. 45, 24), which meet one another dor- 
sally and form the remainder of the boundary of the foramen 
magnum. Each is drawn out externally into a strong process, 
which is united below with the quadrate, and above with the 
squamosal by a surface seen in a disarticulated skull to be 
very rough and splintered. In a longitudinal section the 
anterior face of the exoccipital is seen to be closely united 
with the opisthotic. 

The exoccipital is pierced by a number of foramina, four 
lying on the posterior surface. Just external to the foramen 
magnum is a small foramen for the exit of the hypoglossal 
nerve (figs. 44 and 45, XII). External to this is the foramen 
for the pneumogastric (fig. 44, X), while more ventrally still 
is the foramen (fig. 44, 15) through which the internal carotid 
artery enters the skull. Some distance further to the side, 
and more dorsally, is a larger foramen which gives passage 
to the facial nerve and certain blood-vessels. 

In a median longitudinal section of the skull the hypo- 
glossal foramen is seen, and just in front of it a small foramen 
for a vein. Further forwards the long slit-like opening 
between the exoccipital and opisthotic is the internal audi- 
tory meatus (fig. 45, VIII) through which the auditory 
nerve leaves the cranial cavity and enters the internal 
ear. 



SKELETON OF THE CROCODILE. THE CRANIUM. 247 

The supra-occipital (fig. 45, 5) is a small bone which 
takes no part in the formation of the foramen magnum, and is 
closely united in front with the epi-otic. It is characteristic of 
Crocodiles that all the bones of the occipital segment have 
their longer axes placed vertically, and that they scarcely if at 
all appear on the dorsal surface. 

In front of the occipital segment is the parietal segment. 
The dorsal and ventral portions of the two segments are in 
contact with one another, but the lateral portions are widely 
separated by the interposition of the auditory and suspen- 
sorial bones. 

The basisphenoid (fig. 45, 12) is an unpaired wedge- 
shaped bone, united along a deep vertical suture with the basi- 
occipital. The two bones are, however, partially separated in 
the mid-ventral line by a foramen, the opening of the median 
Eustachian canal, which leads into a complicated system of 
Eustachian passages ultimately communicating with the tym- 
panic cavity. 

The dorsal surface of the basisphenoid is well seen in a 
section of the skull, but owing to the way it tapers ventrally, 
it appears on the ventral surface only as a very narrow strip 
of bone wedged in between the basi-occipital and pterygoids. 
In a lateral view it is seen to be drawn out in front into an 
abruptly truncated process, the rostrum, which forms part of 
the interorbital septum. On the anterior part of the dorsal 
surface is a deep pit, the pituitary fossa or sella turcica, 
at the base of which are a pair of foramina, through which 
the carotid arteries pass. Dorso-late rally the basisphenoid 
articulates with the alisphenoids. 

The alisphenoids (fig. 45, 13) are a pair of irregular bones 
which arise from the basisphenoid antero-laterally, and are 
united dorsally with the parietal, frontal, and postfrontals. 
They bound most of the anterior part of the brain case, 
and each presents on its inner face a deep concavity which 
lodges the cerebral hemisphere of its side. Viewed from 



248 



THE VERTEBRATE SKELETON. 



o a 



- 




' s 



HCO HH 

x eoS 



o. S S c 
^ a a o "so 



8.^ 



o.'^3 s 
S 5s o 

p~ r *s rrt r-> 



* "3 "^ 

.2 60 . ^ 



O5 O iH <M 



Tti ,2 r3 ^^ 

rt ^ i ^ O 

- ^ "^ M l_i I 



ee . 

P "a 



SKELETON OF THE CROCODILE. THE CRANIUM. 249 

the ventral side the two alisphenoids are seen to almost 
or quite meet one another immediately below the frontal, 
and then to diverge, forming an irregular opening partially 
closed by cartilage in the fresh specimen, through which 
the optic nerves leave the cranial cavity. Further back the 
alisphenoids meet one another for a narrow area, and then 
diverge again, so that between each and the rostrum of 
the basisphenoid there appears an opening (fig. 44, III, VI) 
through which the oculomotor and abducens nerves leave 
the cranium. Further back still each is united for a short 
space with the basisphenoid, pterygoid and quadrate, and 
then becomes separated from the quadrate by a large foramen, 
the foramen ovale (fig. 44, V), through which the whole of 
the trigerninal nerve passes out. 

The dorsal portion of the parietal segment is formed by 
the parietal (fig. 45, 4), which though double in the embryo, 
early comes to form a single bone. It extends over the 
posterior part of the cranial cavity, and is continuous in front 
with the frontal, behind with the supra-occipital, and laterally 
with the postfrontals, squamosals, alisphenoids, pro-otics and 
epi-otics. It forms the inner boundary of a large rounded 
vacuity on the roof of the skull, the supratemporal fossa. 

The frontal segment is very imperfectly ossified, there 
being no certain representatives of either the ventral member, 
the presphenoid, or the lateral members, the orbitosphenoids. 
On the dorsal side there is, however, a large development 
of membrane bones. There is a large frontal (fig. 45, 3), 
unpaired, except in the embryo, united behind with the 
parietal and postf rental, and drawn out in front into a long 
process which is overlapped by the prefrontals and posterior 
part of the nasals. The frontal ends off freely below, owing 
to the orbitosphenoidal region being unossified, it forms a 
considerable part of the roof of the cranial cavity, but takes 
no part in the formation of the wall. 

Each prefrontal (fig. 45, 14) forms part of the inner wall 



250 THE VERTEBRATE SKELETON. 

of the orbit and sends ventralwards a process which meets 
the palatine. 

The post/rentals (fig. 44, 6) are small bones lying at the 
sides of the posterior part of the frontal. Each is united 
with a number of bones, on its inner side with the frontal and 
parietal, behind with the squamosal, and ventrally with the 
alisphenoid. It also unites by means of a strong descending 
process with an upgrowth from the jugal, and thus forms a 
postorbital bar separating the orbit from the lateral tem- 
poral fossa. The postfrontal forms also part of the outer 
boundary of the supratemporal fossa. 

2. THE SENSE CAPSULES. 

Skeletal capsules occur in connection with each of the three 
special sense organs of sight, of hearing and of smell. 

The Auditory capsules and associated bones. 

Three bones, the epi-otic, opisthotic and pro-otic, 
together form the auditory or periotic capsule of each side. 
They are wedged in between the lateral portions of the occi- 
pital and parietal segments and complete the cranial wall in 
this region. Their relations to the surrounding structures are 
very complicated, and many points can be made out only in 
sections of the skull passing right through the periotic cap- 
sule. The relative position of the three bones is, however, 
well seen in a median longitudinal section. The opisthotic 
early becomes united with the exoccipital, while the epi-otic 
similarly becomes united with the supra-occipital, the pro- 
otic (fig. 45, 7), seen in longitudinal section to be pierced 
by the prominent trigeminal foramen alone remaining 
distinct throughout life. The three bones together surround 
the essential organ of hearing which communicates laterally 
with the deep tympanic cavity by the fenestra ovalis. 

The tympanic cavity, leading to the exterior by the 
external auditory meatus (fig. 44, 16), is well seen in a 



SKELETON OF THE CROCODILE. SENSE CAPSULES. 251 

side-view of the skull ; it is bounded on its inner side by the 
periotic bones, posteriorly in part by the exoccipital, and else- 
where mainly by the quadrate. A large number of canals 
and passages open into it. On its inner side opening ventro- 
anteriorly is the fenestra ovalis, opening ventro-posteriorly 
the internal auditory meatus (fig. 45, VIII), while dorsally 
there is a wide opening which forms a communication through 
the roof of the brain-case with the tympanic cavity of the 
other side. On its posterior wall is the prominent foramen 
through which the facial nerve passes on its way to its final 
exit from the skull through the exoccipital, this foramen is 
bounded by the quadrate, squamosal, and exoccipital. 

The opening of the fenestra ovalis is in the fresh skull 
occupied by the expanded end of the auditory ossicle, the 
columella, whose outer end articulates by a concave facet 
with a trifid extracolumellar cartilage which reaches the 
tympanic membrane. The lower process of this extracolumella 
passes into a cartilaginous rod which lies in a canal in the 
quadrate and is during life continuous with Meckel's cartilage 
within the articular bone of the mandible. 

The columella and extracolumella are together homologous 
with the chain of mammalian auditory ossicles. 

The Optic capsules and associated bones. 

Two pairs of bones are associated with the optic capsules, 
viz. the lachrymals and the supra-orbitals. The lachrymal 
(fig. 44, 3) is a fairly large flattened bone lying wedged in 
between the maxilla, nasal, jugal, and prefrontal. It forms a 
considerable part of the anterior boundary of the orbit, and is 
pierced by two foramina. On the orbital edge is a large hole 
leading into a cavity within the bone which lodges the naso- 
lachrymal sac, and communicates with the narial passage by 
a wide second foramen near the anterior end of the bone. 
The supra-orbital is a very small loose bone lying in the eyelid 
close to the junction of the frontal and prefrontal. 



252 THE VERTEBRATE SKELETON. 

The Olfactory capsules and associated bones. 

Two pairs of membrane bones, the vomers and nasals, are 
developed in association with the olfactory organ, iDut the 
mesethmoid is not ossified. 

The vomers form a pair of delicate bones, each consisting of 
a vertical plate (fig. 45, 15), which with its fellow separates 
the two narial passages, and of a horizontal plate which forms 
much of their roof. The vomers articulate with one another 
and with the pterygoids, palatines, and maxillae. 

The nasals (fig. 45, 2) are very long narrow bones extend- 
ing along the middle line from the frontal almost to the 
anterior nares. They are continuous laterally with the pre- 
maxillae, maxillae, lachrymals and prefrontals. They form 
the roof of the narial passages. 

3. THE UPPER JAW AND SUSPENSORIAL APPARATUS. 

These are enormously developed in the Crocodile and are 
firmly united to the cranium. It will be most convenient to 
begin by describing the bones at the anterior end of the jaw 
and to work back thence towards the brain-case. The most 
anterior bones are the premaxillae. The premaxillae (figs. 44 
and 45, 1) are small bones, each bearing five pairs of teeth, 
set in separate sockets in their alveolar borders. They con- 
stitute almost the whole of the boundary of the anterior 
nares, which are confluent with one another and form a 
large semicircular opening in the roof of the skull, leading 
into the wide narial passage. They are also partially sepa- 
rated from one another in the ventral middle line, by the 
small anterior palatine vacuity (fig. 43, A, 8). They form 
the anterior part of the broad palate. The alveolar border 
on each side between certain of the teeth is marked by pits 
which receive the points of the teeth of the other jaw. The 
first pair of these pits in the premaxillae are often so deep as 
to be converted into perforations. Pits of the same character 
occur between the maxillary and mandibular teeth. 



THE SKELETON OF THE CROCODILE. 



253 




- 

'= == = 1 * 
; s. x iz-E 1 ^ 



&4 r-i si vi tf is ^ e- - 



254 THE VERTEBRATE SKELETON. 

The maxillae (tigs. 43, A, 2 and 44, 2) are a pair of very 
large bones and bear the remaining teeth of the upper jaw, 
set in sockets along their alveolar borders. On the dorsal 
side each maxilla is continuous with the premaxilla, nasal, 
lachrymal, and jugal, while ventrally it meets its fellow in a 
long straight suture and forms the greater part of the long 
bony palate. The maxillae are separated in the middle line 
posteriorly by processes from the palatines, while further back 
they meet the transpalatines. The internal or nasal surface, 
like that of the premaxilla, is excavated by a deep longitudi- 
nal groove, the narial passage. In a ventral view of the 
skull a number of small openings (fig. 43, A, 21) are seen 
close to the alveolar border, these are the openings of small 
vascular canals which lead into the alveolar sinus, a passage 
traversing the maxilla, and transmitting the superior max 
illary branch of the trigeminal nerve and certain blood-vessels. 
This alveolar sinus opens posteriorly by the more external of 
the two large holes in the maxilla, which lie close to the 
anterior edge of the posterior palatine vacuity, to be described 
immediately. The more internal of these holes, on the other 
hand, leads into a cavity lodging the nasal sac. Behind the 
maxillae the completeness of the palate is broken up by the 
large oval posterior palatine vacuities (fig. 43, A, 7) ; 
these are separated from one another in the middle line by the 
palatines, and are bounded elsewhere by the maxillae, trans- 
palatines, and pterygoids. 

The palatines (fig. 43, A, 3) are long and rather narrow 
bones interposed between the maxillae in front and pterygoids 
behind. They meet one another in a long suture and form 
much of the posterior part of the palate, while the whole length 
of their dorsal surface contributes to the floor of the narial 
passage. The dorsal surface of each bone is also drawn out 
on its outer side into a prominent ridge which forms much of 
the side and roof of the narial passage, being in contact with 
the vomer and pterygoid, and at one point by means of a short 



SKELETON OF THE CROCODILE. THE SKULL. 255 

ascending process with the descending process of the pre- 
frontal. 

The pterygoids (figs. 43, A, 4, and 45, 11) are a pair of 
large bones, each consisting of a median more or less vertical 
part, which becomes ankylosed to its fellow in the middle 
line early in life, and of a wide horizontal part which meets 
the transpalatine. They completely surround the posterior 
nares (fig. 43, A, 5) and their median portions form the whole 
boundary of the posterior part of the narial passage, and assist 
the palatines and vomers in bounding the middle part. The 
horizontal parts form the posterior part of the secondary palate, 
while the dorsal surface of each looks into the pterygoid fossa, 
a large cavity lying below the quadrate and quadratojugal at 
the side of the skull. The lateral margin adjoining the trans- 
palatine is in the fresh skull terminated by a plate of cartilage 
against which the mandible plays. Dorsally the pterygoid 
articulates with the basisphenoid, quadrate, and alisphenoid. 

The transpalatines (fig. 44, 11) connect the pterygoids with 
the jugals and maxillae, articulating with each of the three 
bones by a long pointed process. The jugal process meets also 
a down-growth from the postfrontal. 

The jugals or molars (fig. 44, 5) are long somewhat flat- 
tened bones which are united to the lachrymals and maxillae 
in front, while passing backwards each is united behind to the 
quadratojugal (fig. 44, 12), the two forming the infratemporal 
arcade which constitutes the external boundary of the orbit 
and lateral temporal fossa. The jugal is united below to the 
transpalatine, and the two bones together form an outgrowth, 
which meeting that from the postfrontal forms the postorbital 
bar, and separates the orbit from the lateral temporal fossa. 
The quadratojugals are small bones and are united behind 
with the quadrates. 

The quadrate (figs. 43, A, 13 and 44, 8) of each side is 
a large somewhat flattened bone firmly fixed in among the 
other bones of the skull. It is terminated posteriorly by an 



256 THE VERTEBRATE SKELETON. 

elongated slightly convex surface, coated with cartilage in the 
fresh skull, by which the mandible articulates with the cranium. 
The dorsal surface of the quadrate is flat behind, further for- 
wards it becomes much roughened and articulates with the 
exoccipital and squamosal ; further forwards still it becomes 
marked by a deep groove which forms the floor of the ex- 
ternal auditory meatus and part of the tympanic cavity. 
The anterior boundary of the quadrate is extremely irregu- 
lar, it is united dorsally with the postfrontal, pro-otic, and 
squamosal, and more ventrally with the alisphenoid. The 
smooth ventral surface looks into the pterygoid fossa. In 
front the quadrate forms the posterior boundary of the supra- 
temporal fossa and foramen ovale, and is continuous with the 
alisphenoid, while it sends down a thin plate meeting the 
pterygoid and basisphenoid. On the inner side of the dorsal 
surface of the quadrate near the condyle, is a small foramen 
which leads into a tube communicating with the tympanic 
cavity, by a foramen lying in front of and ventral to that for 
the exit of the facial nerve. By this tube air can pass from 
the tympanic cavity into the articular bone of the mandible. 

The squamosal (fig. 44, 7) meets the quadrate and exoccipital 
below, and forms part of the roof of the external auditory 
meatus, while above it forms part of the roof of the skull and 
has a pitted structure like that of the other bones of the roof. 
It is continuous with the postfrontal in front, forming with 
it the supratemporal arcade which constitutes the outer 
boundary of the supratemporal fossa. It meets also the 
parietal on its inner side, forming the post-temporal bar, the 
posterior boundary of the supratemporal fossa. 

It may be useful to recapitulate the large vacuities in the 
surface of the Crocodile's cranium. 

Dorsal surface. 

1. The Supratemporal fossae. Each is bounded in- 
ternally by the parietal, behind by the post-temporal bar 
formed by the parietal and squamosal, and externally by the 



SKELETON OF THE CROCODILE. THE SKULL. 257 

supratemporal arcade formed by the squamosal and post- 
frontal. The postfrontal meets the parietal in front and forms 
the anterior boundary of the supratemporal fossa. 

2. The Lateral temporal or infratemporal fossae. 
These lie below and to the outer side of the supratemporal 
fossae. Each is bounded dorso-internally by the supratemporal 
arcade ; and behind by a continuation of the post-temporal bar 
formed by the quadrate and quadra tojugal. The external 
boundary is the infratemporal arcade formed of the quad- 
ratojugal and jugal, while in front the fossa is separated from 
the orbit by the postorbital bar formed by the junction of 
outgrowths from the postfrontal and jugal. 

3. The Orbits. Each is bounded behind by the post- 
orbital bar, externally by the jugal forming a continuation of 
the infratemporal arcade, in front by the lachrymal, and inter- 
nally by the frontal and prefrontal. 

4. The Anterior nares. These form an unpaired open- 
ing bounded by the premaxillae. 

Posterior surface. 

5. The Foramen magnum. The exoccipitals form the 
chief part of its boundary, but part of the ventral boundary 
is formed by the basi-occipitaL 

6. The Pterygoid fossae. These form a pair of large 
cavities at the sides of the occipital region of the skull. The 
dorsal boundary is formed by the quadrate and quadratojugal, 
the ventral by the pterygoid, the internal chiefly by the quad- 
rate, pterygoid, alisphenoid, and basisphenoid. The transpala- 
tine forms a small part of the external boundary which is in- 
complete. 

Ventral surface. 

7. The Posterior nares.. These form a median unpaired 
opening (fig. 43, A, 5) bounded by the pterygoids. 

8. The Posterior palatine vacuities. Each is 
bounded by the maxilla in front, the maxilla and transpalatine 

R. 17 



258 THE VERTEBRATE SKELETON. 

externally, the transpalatine and pterygoid behind, and the 
palatine on the inner side (fig. 43, A, 7). 

9. The Anterior palatine vacuity. This is unpaired 
and is bounded by the premaxillae (fig. 43, A, 8). 

(b) THE LOWER JAW OR MANDIBLE. 

The mandible is a strong compact bony structure formed 
of two halves or rami, which are suturally united at the 
symphysis in the middle line in front. Each ramus is formed 
of six separate bones. 

The most anterior and largest of these is the dentary (figs. 
44, 20, and 45, 18), which forms the symphysis, and greater part 
of the anterior half of the jaw, and bears along the outer part 
of its dorsal border a number of sockets or alveoli in which 
the teeth are placed. Lying along the inner side of the dentary 
is a large splint-like bone, the splenial (fig. 45, 19), which does 
not extend so far forwards as the symphysis, and is separated 
from the dentary posteriorly by a large cavity. Forming the 
lower part of all the posterior half of the jaw is the large 
angular (figs. 44, 22, and 45, 20), which underlies the posterior 
part of the dentary in front and sends a long process below that 
bone to the splenial. On the inner side of the jaw there is an 
oval vacuity, the internal mandibular foramen (fig. 45, 28), 
between the angular and the splenial ; through this pass blood- 
vessels and branches of the inferior dental nerve. Lying 
dorsal to the angular is another large bone, the supra-angular 
(figs. 44, 18, and 45, 21). It extends back as far as the pos- 
terior end of the jaw and forwards for some distance dorsal 
to the dentary and splenial. It forms part of the posterior 
margin of a large vacuity, the external mandibular foramen, 
which is bordered above and in front by the dentary and below 
by the angular ; it gives passage to the cutaneous branch of 
the inferior dental nerve. The concave surface for articulation 
with the mandible and much of the posterior end of the jaw i 
formed by a short but solid bone, the articular (fig. 45, 22), 



SKELETON OF THE CROCODILE. THE HYOID. 259 

which in young skulls rather readily becomes detached. The 
remaining mandibular bone is the coronoid (fig. 45, 23), a very 
small bone of irregular shape attached to the angular below, 
and to the supra-angular and splenial above. 

(c) THE HYOID. 

The hyoid of the Crocodile consists of a wide flattened 
plate of cartilage, the basilingual plate or body of the 
hyoid, and a pair of cornua. 

The basilingual plate (fig. 53, 1) is rounded anteriorly 
and marked by a deep notch posteriorly. The cornua (fig. 
53, 3), which are attached at a pair of notches near the middle 
of the outer border of the basilingual plate, are partly ossified, 
but their expanded ends are formed of cartilage. They pass 
at first backwards and then upwards and inwards. They 
are homologous with part of the first branchial arches of 
Selachians. 

The columella and extra-columella have been already de- 
scribed (p. 251). 

C. THE RIBS AXD STERXUM. 

Thoracic ribs. 

The Crocodile has ten pairs of thoracic ribs, all except 
the last one or two of which consist of three parts, a verte- 
bral rib, an intermediate rib and a sternal rib. 

Of the vertebral ribs the third mav be taken as a type, 
it consists of a curved bony rod which articulates proximally 
with the transverse process of the vertebra by two facets. 
The terminal one of these, the capitulum or head, articulates 
with a notch on the side of the transverse process; the other, 
the tuberculum, which lies on the dorsal surface a short 
distance behind the head, articulates with the end of the trans- 
verse process. From near the distal end an imperfectly ossified 
uncinate process (see p. 190) projects backwards. 

The intermediate ribs are short and imperfectly ossified : 
they are united with the sternal ribs (fig. 46, 3), which are large, 

172 



260 THE VERTEBRATE SKELETON. 

flattened, likewise imperfectly ossified structures, and articu- 
late at their distal ends with a pair of long divergent xiphi- 
sternal horns (fig. 46, 5), which arise from the posterior end 
of the sternum proper. The last pair of sternal ribs are at- 
tached to the preceding pair, not to the xiphisternal horns. 

The first and second vertebral ribs differ from the others in 
the fact that the tuber culum forms a fairly long outstanding 
process. 

Cervical ribs. 

Movable ribs are attached to all the cervical as well as to the 
thoracic vertebrae. Those borne by the atlas and axis are long, 
narrow structures attached by a fairly broad base, and tapering 
gradually. The ribs borne by the third to seventh cervical 
vertebrae are shaped like a T with a double base, one limb of 
which, corresponding to the tuberculum (fig. 41, 7), articulates 
with a shoi't transverse process arising from the neural arch, 
while the other, corresponding to the capitulum, articulates with 
a surface on the centrum. The ribs attached to the eighth and 
ninth cervical vertebrae are intermediate in character between 
the T-shaped ribs and the ordinary thoracic ribs. The anterior 
limb of the T is shortened, the posterior one is drawn out, 
forming the shaft of the rib. The distal portion of the rib of 
the ninth cervical vertebra is unossified. 

The Sacral ribs have been described in connection with 
the sacral vertebrae. 

THE STERNUM. 

The sternum, of Crocodiles is a very simple structure, con- 
sisting of a plate of cartilage (fig. 46, 2) lying immediately 
dorsal to the interclavicle, and drawn out posteriorly into a 
pair of long xiphisternal horns (fig. 46, 5). 

THE ABDOMINAL SPLINT RIBS. 

Lying superficially to the recti muscles of the ventral body- 
wall, behind the sternal ribs, are seven or eight series of 



SKELETON OF THE CROCODILE. THE STERNUM. 261 



-2 



.--5 




FIG. 46. STEKSTJH AND ASSOCIATED MEJIBRA>TE BONES OF A CROCODILE 
(C. palustrig) x . (Brit. Mas.) 

The last pair of abdominal ribs which are united with the epipubes by 
a plate of cartilage have been omitted. 

1. interclavicle. 4. abdominal splint rib. 

2. sternum. 5. xiphisternal horn. 

3. sternal rib. 



262 



THE VERTEBRATE SKELETON. 



slender curved bones, the abdominal ribs (fig. 46, 4). Each 
series consists of four or more bones, arranged in a V-like 
form with the angle of the V directed forwards. They show a 
considerable amount of variability in number and character. 
They are really membrane bones, and are in no way homolo- 
gous with true ribs, but correspond rather with the more 
posterior of the bones constituting the plastron of Chelonia. 

2. THE APPENDICULAR SKELETON. 

This includes the skeleton of the two pairs of limbs and 
their respective girdles. 




FIG. 47. LEFT HALF OF THE PECTORAL GIRDLE OF AN ALLIGATOR (Caiman 
latirostris) x f . (Brit. Mus. ) 

1. scapula. 3. interclavicle. 

2. coracoid. 4. glenoid cavity. 

THE PECTORAL GIRDLE. 

The pectoral girdle of the Crocodile is less complete than is 
that of most reptiles. It consists of a dorsal bone, the 



SKELETON OF THE CROCODILE. PECTORAL GIRDLE. 263 

scapula, and a ventral bone, the coracoid, with a median 
unpaired element, the interclavicle : but there is no separate 
representative either of the clavicle or precoracoid. 

The scapula (fig. 47, 1) is a large bone, flattened and ex- 
panded above where it is terminated by an unossified margin 
the suprascapula, and thickened below where it meets the 
coracoid. The scapula forms about half the glenoid cavity 
(fig. 47, 4) for articulation with the humerus, and has the 
lower part of its anterior border drawn out into a roughened 
ridge. 

The coracoid (fig. 47, 2) is a flattened bone, much ex- 
panded at either end ; it bears on its upper posterior border a 
flattened surface which forms half the glenoid cavity, and is 
firmly united to the scapula at its dorsal end. Its ventral end 
meets the sternum. 

The interclavicle (figs. 46, 1, and 47, 3) is a long narrow 
blade-shaped bone lying along the ventral side of the sternum ; 
about a third of its length projects beyond the sternum in 
front. 

THE ANTERIOR LIMB. 

This is as usual divisible into three portions, the upper 
arm, fore-arm and manus. 

The upper arm or brachium contains one bone, the 
humerus. 

The humerus (fig. 48, A, 1) is a fairly long stout bone, 
considerably expanded at either end. The proximal end or head 
is evenly rounded and is formed by an epiphysis ossifying from 
a centre different from that forming the shaft. It articulates 
with the glenoid cavity. The shaft bears on the flexor surface, 
at some little distance behind the head, a prominent rounded 
protuberance, the deltoid ridge. The distal end or trochlea 
is also formed by an epiphysis and is partially divided by a 
groove into two convex surfaces ; it articulates with the two 
bones of the fore-arm, the radius and ulna. 



264 



THE VERTEBRATE SKELETON. 



B 




FIG. 48. 



r 20 



A, EIGHT ANTEBIOB, AND B, EIGHT POSTEEIOE LIMB OF A YOUNG 

ALLIGATOE (Caiman latirostris). (Brit. Mus.) 
A x . B x about . 



1. humerus. 10. 

2. radius. 

3. ulna. 11. 

4. radiale. 12. 

5. ulnare. 13. 

6. pisiform. 14. 

7. patch of cartilage representing 15. 

carpalia 1 and 2 ; between 

it and the radiale should be 16. 

another flattened patch, the 17. 

ceutrale. 18. 

8. carpalia 3, 4, and 5 (fused). 19. 

9. first metacarpal. 20. 

21. 



proximal phalanx of second 

digit. 

second phalanx of fifth digit, 
femur, 
tibia, 
fibula, 
tibiale, intermedium and cen- 

trale (fused), 
fibulare. 

tarsalia 1, 2, and 3 (fused), 
tarsalia 4 and 5 (fused), 
first metatarsal. 
nngual phalanx of second digit, 
fifth metatarsal. 



SKELETON OF THE CROCODILE. THE MANUS. 265 

The radius and ulna are nearly equal in size and each 
consists of a long shaft terminated at either end by an epi- 
physis. 

The radius (fig. 48, A, 2) or pre-axial bone is slightly the 
smaller of the two. It has a straight -cylindrical shaft and is 
slightly and nearly evenly expanded at either end. The proxi- 
mal end which articulates with the humerus is flat or slightly 
concave, the distal end which articulates with the carpus is 
slightly convex. 

The ulna (fig. 48, A, 3) or postaxial bone is a curved bone 
rather larger than the radius. Its proximal end is large and 
convex, but is not drawn out into an olecranon process. 

The Manus consists of the carpus or wrist, and the 
hand. 

The Carpus. This differs considerably from the more 
primitive type met with in the Turtle. It consists of six 
elements arranged in a proximal row of three and a distal row 
of two, with one intervening. The bones of the proximal row 
are the radiale, the ulnare, and the pisiform. The radiale 
(fig. 48, A, 4) is the largest bone of the carpus : it is a some- 
what hour-glass shaped bone, with its ends formed by flattened 
epiphyses. It articulates by its proximal end with the whole 
of the radius, and partly also with the ulna, and by its 
distal end with the centrale. 

The ulnare (fig. 48, A, 5) is a smaller bone, also some- 
what hour-glass shaped : it articulates proximally with the 
pisiform and radiale, not quite reaching the ulna. The third 
bone of the proximal row is the pisiform (fig. 48, A, 6), an 
irregular bone, articulating with the ulna, radiale, and fifth 
metacarpal. The centrale is a flattened cartilaginous element 
applied to the distal surface of the radiale. 

The distal row of carpals consists of two small structures. 
The first of these forms a small cartilaginous patch, which is 
wedged in between the first and second metacarpals, the 



266 THE VERTEBRATE SKELETON. 

centrale and the bone representing carpalia 3, 4 and 5 ; this 
cartilaginous patch represents carpalia 1 and 2 (fig. 48, A, 7). 
The bone representing carpalia 3, 4 and 5 is a good deal 
larger, rounded, and well -ossified ; it articulates with the 
ulnare, the pisiform, and the third, fourth, and fifth meta- 
carpals. 

The hand. Each of the five digits consists of an elongated 
metacarpal, terminated at each end by an epiphysis, and of a 
varying number of phalanges. The terminal phalanx of each 
digit has an epiphysis only at its proximal end, the others have 
them at both ends. 

The first digit, or pollex, is the stoutest, and has two 
phalanges, the second has three, the third four, the fourth 
three, and the fifth two. The terminal phalanx of each of the 
first three digits is pointed and sheathed in a horny claw ; and 
is also marked by a pair of prominent lateral grooves. 

THE PELVIC GIRDLE. 

The pelvic girdle of the Crocodile consists of four parts, a 
dorsal element, the ilium, an anterior ventral element, the 
pubis, a posterior ventral element, the ischium, and an 
accessory anterior ventral element, the epipubis. All except 
the epipubis take part in the formation of the acetabulum, 
which is perforated by a prominent hole. 

The ilium (fig. 49, 1) is a thick strong bone, firmly united 
on its inner side with the two sacral ribs. Its dorsal border 
is rounded, its ventral border bears posteriorly two irregular 
surfaces, completed by epiphyses, which are united respectively 
with the ischium and pubis. 

The ischium (fig. 49, 2) the largest bone of the pelvis, 
is somewhat contracted in the middle and expanded at either 
end. Its proximal end, which is formed by an epiphysis, 
bears two surfaces, one of which is united to the ilium, 
while the other forms part of the acetabulum. The anterior 
border is also drawn out dorsally into a strong process, which 



SKELETON OF THE CROCODILE. PELVIC GIRDLE. 267 

is terminated by a convex epiphysis, and is united to the 
pubis. The ventral end of the ischium forms a flattened blade, 
meeting its fellow in a median symphysis. 

The pubis (fig. 49, 3) is much smaller than either the ilium 
or ischium ; it forms a small patch of unossitied cartilage, in- 
terposed between the anterior parts of the ilium and ischium. 




FIG. 49. PELVIS AND SACBCM OF AN ALLIGATOR (Caiman latirostri$) x 
(Brit. Mus.) 



1. ilium. 

2. ischium. 

3. true pubis. 

4. epipubis (so-called pubis). 

5. acetabular foramen. 



6. neural spines of sacral verte- 

brae. 

7. symphysis ischii. 

8. process bearing prezygapo- 

physis. 



The epipubis (fig. 49, 4) is a large bone with a thickened 
proximal end, which is loosely articulated to the ischium, and 
a flattened expanded distal end, which is united with its fellow, 
and with the last pair of abdominal ribs by a large plate of 
cartilage. This bone is generally described as the pubis. 



268 THE VERTEBRATE SKELETON. 

THE POSTERIOR LIMB. 

This is as usual divisible into three portions, the thigh, 
the crus or shin, and the pes. 

The thigh is formed by the femur (fig. 48, JB, 12), a 
moderately long stout bone, not unlike the humerus ; it arti- 
culates with the acetabulum by a fairly prominent rounded 
head. The distal end articulating with the tibia and fibula 
is also expanded, and is partially divided into equal parts by 
anterior and posterior grooves. The flexor surface bears a 
fairly prominent trochanteric ridge. Each end of the femur 
is formed by an epiphysis. 

The crus or shin includes two bones, the tibia and 
fibula. Both are well developed, but the tibia is considerably 
the larger of the two. 

The tibia (fig. 48, B, 13) is a strong bone with a flattened 
expanded proximal end articulating with almost the whole of 
the end of the femur, and a similarly expanded distal end 
articulating with a bone representing the fused astragalus and 
centrale. 

The fibula (fig. 48, B, 14) is flattened proximally, and 
articulates with only quite a small part of the femur, while 
distally it is more expanded, and articulates with the fibulare 
(calcaneum) and with a facet on the side of the fused astra- 
galus and centrale. 

The Pes consists of the tarsus or ankle, and the foot. 

The Tarsus. This, like the carpus, is much, reduced and 
modified from the primitive condition. It consists of only 
four bones, arranged in two rows of two each. The two 
bones of the proximal row are much larger than are those of 
the distal row. The pre-axial of them (fig. 48, B, 15) repre- 
senting the fused astragalus (tibiale and intermedium) and 
centrale, articulates proximally with the tibia and fibula, and 
distally with the first metatarsal, and a small bone representing 
the first three tarsalia. The post-axial bone, the calcaneum 



SKELETON OF THE CROCODILE. THE PES. 269 

(fibulare) (fig. 48, B, 1 6), is drawn out into a prominent posterior 
process forming a heel such as is almost unknown elsewhere 
except in mammals. It articulates with the fibula, the tibiale- 
centrale, and distally with a bone representing the fourth and 
fifth tarsalia, and with the fifth metatarsal. 

The two bones forming the distal row of tarsals are both 
small and rounded ; one represents the first three tarsalia fused 
together, the other tarsalia 4 and 5. 

The Foot. The foot has five digits, but the fifth is much 
reduced, consisting only of a short metatarsal. The first four 
metatarsals are all long bones, slightly expanded at each 
end, and terminated by small epiphyses. The first digit has 
two phalanges, the second three, the third four, and the fourth 
five. The terminal or ungual phalanx in each instance is 
grooved and pointed, and in the case of the first three digits 
bears a horny claw. The ungual phalanx progressively de- 
creases in size from the first to the fourth. The fifth digit 
consists only of a small, somewhat square metatarsal (fig. 48, 
B, 21), attached to the bone representing the fused fourth and 
fifth tarsalia. 



CHAPTER XVI. 

GENERAL ACCOUNT OF THE' SKELETON IN 
REPTILES. 

EXOSKELETON. 

The exoskeleton both epidermal and dermal is exceedingly 
well developed in reptiles. 

EPIDERMAL EXOSKELETON. 

This generally has the form of overlapping horny scales 
which invest outgrowths of the dermis, and are found covering 
the whole body in most Rhynchocephalia, Ophidia, and Lacer- 
tilia, and many Crocodilia. In the Ophidia the ventral surface 
of the tail is commonly covered by a double row of broad scales, 
while the ventral surface of the precaudal part of the body is 
covered by a single row. In the burrowing snakes (Typhlo- 
pidae) and some sea snakes (Hydrophidae) these broad scales 
do not occur, the scales of the ventral surface being similar to 
those of the dorsal. 

In the Chelonia with the exception of Dermochelys, Trionyx 
and their allies there is a well-developed system of horny shields 
having a regular arrangement which has been described in the 
account of the Turtle's skeleton 1 . 

The rattle of the rattlesnake is an epidermal structure 
formed of several loosely articulated horny rings, produced by 
the modification of the epidermal covering of the end of the 
tail, which instead of being cast off when the rest of the outer 
skin is shed is retained loosely interlocked with the adjoining 

1 See pp. 214 and 215. 



THE SKELETON IN* REPTILES. EXOSKELETON. -71 

ring or joint. New rings are thus periodically added to the 
base of the rattle, and in old animals the terminal ones wear 
away and are lost. 

Horny claws occur on the ends of some or all of the digits 
in most living reptiles. 

Owen's Chameleon bears three epidermal horns, one arising 
from the nasal and two from the frontal region. 

In the Chelonia, some of the Theromorpha such as "'/>- 
nodon and Dicynodon, probably also in the Pterosauria and 
Polyonax among the Dinosaurs, the jaws are more or less 
cased in horny beaks. The horny beaks of Chelonia are 
variable ; sometimes they have cutting edges, sometimes they 
are denticulated, sometimes they are adapted for crushing. 

DERMAL EXOSKELETON. 

Nearly all Crocodilia, many Dinosauria, some Rhynchoce- 
phalia and Pythonornorpha, and some Lacertilia such as Tiliqua, 
Si-incus and Anguis have a dermal exoskeleton of bony scutes, 
developed below and corresponding in shape to the epidermal 
scales. Sometimes as in Caiman scferaps, Jacare and Teleo- 
saurus, the scutes completely invest the body, being so 
arranged as to form a dorsal and a ventral shield, and a con- 

O * 

tinuous series of rings round the tail. In Crocodilus they are 
confined to the dorsal surface, and in Alligator to the dorsal 
and ventral surfaces. The scutes of some extinct forms articu- 
late with one another by a peg and socket arrangement as in 
some Ganoid fish. 

The carapace of most Chelonia is a compound structure, 
being partly endoskeletal and formed from the ribs and verte- 
brae, partly from plates derived from the dermal exoskeleton. 
The common arrangement is seen in fig. 36. All the surface 
plates are probably exoskeletal in origin, but united with the 
ventral surfaces of the costal and neural plates respectively are 
the expanded ribs and neural arches of the vertebrae. 

The plastron in the common genus Chelone (fig. 37) 



272 THE VERTEBRATE SKELETON. 

includes nine plates of bone, one unpaired and four pairs ; 
they will be referred to in connection with the ribs and pec- 
toral girdle. 

In the Leathery Turtle (Dermochelys) the carapace and 
plastron differ completely from those of any other living 
form. The carapace consists of a number of polygonal ossifi- 
cations fitting closely together and altogether distinct from the 
vertebrae and ribs. The plastron is imperfectly ossified, and 
not united with the pelvis, and the whole surface of both 
carapace and plastron is covered with a tough leathery skin, 
without horny shields. 

Some of the extinct Dinosauria have an enormously de- 
veloped dermal exoskeleton. Thus in Stegosaurus and Omo- 
saurus the dorsal surface is provided with flattened plates or 
with spines reaching a length of upwards of two feet. In 
Polacanthus the posterior part of the body is protected by a 
bony shield somewhat recalling that of the little armadillo 
Chlcvmydophorus. No exoskeleton is known in Ichthyosauria, 
Sauropterygia, Pterosauria, many Dinosauria and Theromorpha, 
and some Lacertilia, such as Chamaeleon and Amphisbaena. 

TEETH. 

The teeth of reptiles are generally well developed, and in 
the great majority of forms are simple conical structures, 
uniform in character, generally somewhat recurved, and often 
with serrated edges. Another common type of tooth is that 
with a laterally compressed triangular crown provided with 
a double cutting edge which may or may not be serrated. The 
teeth are mainly formed of dentine, with usually an external 
layer of enamel, and often a coating of cement on the root. 
Vasodentine is found below the dentine in lyuanodon. The 
teeth of reptiles never have the enamel deeply infolded, nor 
do they have double roots. 

Teeth may be present not only on the jaw-bones, but as in 
many Squamata, also on the palatines, pterygoids or vomers. 






THE SKELETON IN REPTILES. THE TEETH. 273 

The method by which they are attached to the bones varies 
much. Sometimes as in Iguana and some other lizards, they 
are pleurodont l , sometimes they are acrodont 1 , as in the Rhyn- 
chocephalia, Pythonomorpha, Ophidia and some Lacertilia such 
as A gamut. Again they may be set in a continuous groove 
as in the Ichthyosauria and young Crocodilia. Finally the 
teeth may be thecod&nt or placed in distinct sockets as in the 
Therornorpha, Sauropterygia, adult Crocodilia, Sauropoda and 
Theropoda. In Iguanodon the teeth are set in shallow sockets 
in a groove one side of which is higher than the other ; the 
method of attachment thus shows points of resemblance to 
the thecodont condition, the pleurodont condition, and that 
met with in the Ichthyosauria. 

In Ichthyosaurus the teeth are marked by a number of 
vertical furrows, and it is from a furrow of this nature greatly 
enlarged and converted into a tube that the channel down 
which flows the poison of venomous snakes is derived. 

In most reptiles the dentition is more or less homodont. 
The only reptiles in which a definite heterodont dentition is 
known are the extinct Theromorpha, and in them the teeth 
vary greatly. Thus Udenodon is toothless, the jaws having 
been probably cased in a horny beak. In Dicytiodon the jaws 
are likewise toothless with the exception of a pair of perma- 
nently growing tusks borne by the maxillae. Dicynodon is the 
only known reptile whose teeth have permanently growing 
pulps. In Pariasaurus the teeth are uniform and very nume- 
rous, and though placed in distinct sockets are ankylosed to 
the jaw. In Galesaurus and Cynognathus three kinds of teeth 
can be distinguished, slender conical incisor-like teeth, large 
canine-like teeth, and cheek teeth with two or three cusps. 
The teeth in Galesaurus are confined to the jaws, in Placodus 
and its allies, however, large flat crushing teeth are attached to 
the palatines as well as to the jaw-bones, and in Pariasaurus 
the vomer, palatine and pterygoid all bear teeth as well as the 

1 These terms are defined on p. 199. 
R. 18 



274 



THE VERTEBRATE SKELETON. 



jaw bones. The upper jaw of Sphenodon and other Rhyn- 
chocephalia is provided with two parallel rows of teeth, one 
borne on the maxillae and one on the palatines, the nian- 
dibular teeth bite in a groove between these two rows. The 
bone of the jaws in Sphenodon is so hard that when the teeth 
get worn away, it can act as a substitute. In the young 
Sphenodon the vomers bear teeth, as they do also in Protero- 
saurus. 

There is generally a continuous succession of teeth through- 
out life, the new tooth coming up below, or partly at the side 
of the one in use, and causing the absorption of part of its 
wall or base. In this way the new tooth comes to lie in the 
pulp cavity of the old one. This method of succession is well 
seen in the Crocodilia. 




3' 



FIG. 50. PBEPAKATION OF PART OF THE BIGHT MANDIBULAR BAMUS OF 
Crocodilus palustris x . (Brit. Mus.) 



1. tooth in use. 

2. fairly old germ of future 

tooth. 



3. symphysial surface of the 
mandible. 



Teeth have been detected in embryos of Trionyx, but 
otherwise no teeth are known to occur in Chelonia, or in 
Pteranodon (Pterosauria), while the anterior part of the jaw 
is edentulous in Iguanodon, Polyonax and some other Dino- 
saurs, and in Rhamphorhynchus. 



THE SKELETON IN REPTILES. VERTEBRAL COLUMN. 275 

EXDOSKELETOX. 

VERTEBRAL COLUMN. 

The vertebral column is commonly divisible into the usual 
five regions, but in the Ophidia, Ichthyosauria, and Amphis- 
baenidae among Lacertilia, only into caudal and precaudal 
regions. In the Chelonia there are no lumbar vertebrae. 

The form of the vertebral centra is very variable. A large 
proportion of extinct reptiles, several entire orders, and the 
earlier and more primitive forms in some of the other groups 
have amphicoelous vertebrae. Vertebrae of this type occur 
in the Theromorpha, Ichthyosauria, most Sauropterygia and 
Rhynchocephalia, and many Dinosauria, also in some of the 
early Crocodilia such as Belodon, Tdeosaurus and Goniopholis, 
and the Geckonidae among Lacertilia, 

The majority of living reptiles have procoelous vertebrae. 
Thus they occur in the Lacertilia (excluding the Geckos), the 
Ophidia, and the Crocodilia, also among extinct forms in the 
Pterosauria and many Dinosauria. On the other hand some 
Dinosauria such as Iguanodon have opisthocoelous cervical 
vertebrae, while others have opisthocoelous thoracic vertebrae. 
The vertebrae of the Ceratopsidae and some Sauropterygia, 
the thoracic vertebrae of Iguanodon, and the sacral vertebrae 
of Crocodilia have flat centra. The first caudal vertebra of 
modern Crocodilia is biconvex, and in the Chelonia all types 
of vertebral centra are found. The cervical vertebrae of 
Sphenodon are noticeable for the occurrence of a small pro- 
atlas, which may represent the neural arch of a vertebra in 
front of the atlas. 

In most reptiles the vertebrae are fully ossified, but in 
some of the more primitive forms the notochord persists in 
the centre of the vertebra (Le. intervertebrally), this is the 
case for instance in many of the Theromorpha and Rhyncho- 
cephalia, and also in the Geckos. In other reptiles it persists 
longest intravertebrally. 

The centrum of each of the caudal vertebrae of most 

182 



276 THE VERTEBRATE SKELETON. 

Lacertilia is traversed by an unossified septum along which it 
readily breaks. 

Chevron bones occur below the caudal vertebrae in Lacertilia, 
Chelonia, Ichthyosauria, many Dinosauria, and Sphenodon, 
articulating with quite the posterior part of the centrum which 
bears them. In Lacertilia and Orocodilia (fig. 41, 3) the axis 
has a well-marked odontoid process. The ventral portions of 
the intervertebral discs are sometimes ossified, forming wedge- 
shaped intercentra, as in Geckos, and the cervical vertebrae of 
Sphenodon. 

In snakes, Theropod Dinosaurs, and the iguanas among 
lizards, the neural arches are provided with zygosphenes, and 
zygantra. 

The neural arches are usually firmly ankylosed to the 
centra, but in the Crocodilia and some Chelonia, Sauropterygia, 
and Dinosauria, the suture between the centrum and neural 
arch persists at any rate till late in life. In the Ichthyosauria 
the neural arches were united to the centra by cartilage only. 

The thoracic vertebrae of some of the Theromorpha (Dime- 
trodon) are remarkable for the extraordinary development of 
the neural spine, and those of Chelonia for the absence of 
transverse processes. 

In living reptiles the number of sacral vertebrae is nearly 
always two, but in the Theromorpha, Dinosauria, and Ptero- 
sauria, as many as five or six bones may be ankylosed together 
in the sacral region. In Crocodiles the two halves of the pelvis 
sometimes articulate with different vertebrae. The vertebrae 
of some of the great Sauropoda are remarkably hollowed out, 
having a large vacuity on each side of the centrum communi- 
cating with a series of internal cavities. The whole structure 
of these vertebrae shows a combination of great strength with 
lightness. 

THE SKULL. 

The reptilian skull is well ossified and the bones are noticeable 
for their density. The true cranium is often largely concealed 



THE SKELETON IX REPTILES. THE SKULL. 277 

by a secondary or false roof of membrane bones, which is best 
seen in the Ichthyosauria and some of the Chelonia. In other 
reptiles the false roof is more or less broken up by vacuities 
exposing the true cranial walls. The ethmoidal region is the 
only one in which much of the primordial cartilaginous cranium 
remains. The lateral parts of the sphenoidal region are also 
as a rule not well ossified. 

In some reptiles, such as most Lacertilia and Chelonia, the 
orbits are separated only by the imperfect interorbital septum, 
while in others, such as the Ophidia, Crocodilia and Amphis- 
baenidae, the cranial cavity extends forwards between the 
orbits. 

In the occipital region all four bones are ossified. The 
great majority of reptiles have a single convex occipital 
condyle, but some of the Theromorpha such as Cynognathus 
have two distinct ^ondyles as in mammals. Sometimes, as 
in Chelonia, Ophidia and Lacertilia, the exoccipitals, as well 
as the basi-occipital, take part in the formation of the single 
condyle ; sometimes, as in Crocodiles, it is formed by the basi- 
occipital alone, as in birds. The relations of the bones to the 
foramen magnum vary considerably, in Chelonia the basi- 
occipital generally takes no part in bounding it, and in the 
Theromorpha, Crocodilia, and Ophidia, the supra-occipital is 
excluded. The parietals are paired in Geckos and Chelonia 
alone among living forms, and .in the extinct Ichthyosauria 
and some Theromorpha ; in all other reptiles they are united. 

The frontals are paired in Ichthyosauria (fig. 32, 5), 
Chelonia, Ophidia, Sphenodon (fig. 52, B, 4) and some extinct 
crocodiles, such as Belodon. They are completely fused in 
living Crocodilia and some Lacertilia and Dinosauria. In 
the gigantic Polyonax they are drawn out into a pair of 
enormous horns, and the parietals and squamosals are greatly 
expanded behind. 

An interparietal foramen occurs in the Theromorpha, the 
Ichthyosauria (fig. 32, 10), Sphenodon, the Sauropterygia and 



278 THE VERTEBRATE SKELETON. 

most Lacertilia. The posterior part of the skull is curiously 
modified in some Chamaeleons, the parietals and supra-occipitals 
being drawn out into a backwardly-projecting sagittal crest 
which unites with the two prolongations from the squamosals. 
In other Chamaeleons (C. bifidus) prolongations of the pre- 
frontals and maxillae form large forwardly-projecting bony 
processes. 

The roof of the skull is characterised by the development 
of pref rentals and postfrontals, which lie respectively near the 
anterior and posterior extremity of the orbit. In Theromorpha, 
Squamata, Crocodilia, and some Dinosauria lachrymals are 
developed. There is a ring of bones in the sclerotic in the 
Ichthyosauria (fig. 32, 15), the Metriorhynchidae among Croco- 
diles and some Rhynchocephalia, Dinosauria, and Pterosauria. 

The pro-otic lies in front of the exocpipital and together 
with the opisthotic forms the hind borcTer of the fenestra 
ovalis. In Chelonia the opisthotic remains separate, in all other 
living reptiles it fuses with the exoccipital. The epi-otic fuses 
with the supra-occipital. 

The parasphenoid, so important in Ichthyopsids, has very 
often disappeared completely ; it is present, however, in the 
Ichthyosauria, the Plesiosauridae, and a number of Squamata, 
in many Ophidia its anterior part forming the base of the 
interorbital septum. 

In the Plesiosauridae and most Lacertilia, but not in the 
Amphisbaenidae, a slender bone, the epipterygoid, occurs unit- 
ing the parietal or the anterior end of the pro-otic with the 
pterygoid. A homologous arrangement occurs in the Ichthyo- 
sauria and some Chelonia. 

In most reptiles a transpalatine occurs, connecting the 
maxilla with the pterygoid, but this is absent in the Chelonia, 
and some Dinosauria, and in the Typhlopidae among snakes. 

The quadrate is always well developed, and except in the 
Squamata is firmly fixed to the surrounding bones. The 
Chamaeleons also, among the Squamata, have a fixed quadrate, 



THE SKELETON IX REPTILES. THE SKULL. 279 

and in them too the quadratojugal is absent. Separate nasal 
bones do not occur in any living Chelonia. 

The vomers are generally paired as in Squamata, some- 
times unpaired as in Chelonia. 




FIG. 51. DORSAL (TO THE LEFT) AXD VEXTRAL (TO THE RIGHT) VIEWS OF 
THE SKULL OF THE Coicsiox SXAKE (Tropidinotus natrix). (After PARKER.) 



1. premaxillae (fused). 

2. anterior nares. 

3. nasal. 

4. prefrontal. 

5. frontal. 

6. parietal 

7. maxilla. 

8. transpalatine. 

9. palatine. 

10. pterygoid. 

11. pro-otic. 

12. exoccipital. 

13. supra-occipital. 

14. opisthotic. 

15. epi-otic. 



16. quadrate. 

17. parasphenoid. 

18. basispbenoid. 

19. basi-occipital. 

20. occipital condyle. 

21. splenial. 

22. dentary. 

23. angular. 

24. articular. 

25. supra-angular. 

26. coronoid. 

27. vomer. 

28. squamosal. 

IX. X foramina for the ninth 

and tenth cranial nerves. 



280 THE VERTEBRATE SKELETON. 

The disposition of the bones of the jaws is subject to 
much modification in the Ophidia in order to adapt them for 
swallowing very large prey. The arrangements again differ 
greatly in the venomous and non-venomous snakes. In the 
non-venomous snakes, such as Python and Tropidonotus, the 
palatine is large and is fixed to the pterygoid which extends 
outwards (fig. 51, 10) so as to be united to the quadrate, and 
is at the same time firmly connected by the transpalatine with 
the maxilla. The quadrate is united to the squamosal, which 
is loosely attached to the cranium. The premaxilla is moder- 
ately developed and bears teeth, and the maxilla forms a long 
bar loosely connected with the rest of the skull. The rami of 
the mandible are united only by an extreme^ elastic ligament. 
It is as regards the maxillae and premaxilrae that the skulls 

of venomous and non-venomous snakes diner most. In the 

^H 

rattlesnake (Crotalus) and other venoinAHfenakes the pre- 
maxilla is extremely small and toothless. The maxilla is 
small and subcylindrical, and is movably articulated to the 
lachrymal, which also is capable of a certain amount of motion 
on the frontal. The maxilla is connected by means of the 
transpalatine with the pterygoid, which in its turn is united 
to the quadrate. When the mouth is shut the quadrate is 
directed backwards, and carrying back the pterygoid and 
transpalatine pulls at the maxilla and causes its palatal face, 
to which the poison teeth are attached, to lie back along the 
roof of the mouth. When the mouth opens the distal end 
of the quadrate is thrust forward, and this necessitates the 
pushing forward of the pterygoid and transpalatine, causing 
the tooth-bearing surface of the maxilla to look downwards 
and the tooth to come into the position for striking. 

The Ophidian skull is also noticeable for the absence of the 
jugals and quadratojugals. In poisonous snakes the- place of 
the jugal is taken by the zygomatic ligament which connects 
the quadrate and maxilla. 

The extent to which the palate is closed in reptiles varies 



THE SKELETON IX REPTILES. THE SKULL. 281 

much. In many reptiles, such as the Squamata and Ichthyo- 
sauria, the palate is not complete, both palatines and pterygoids 
being widely separated in the middle line. In others, such as 
the Crocodilia, Sauropterygia, and Chelonia, there is a more 
or less complete bony palate. In many Chelonia this is 
chiefly formed of the vomer, palatines, and pterygoids, the 
posterior iiares being mainly bounded by the palatines. In 
living Crocodilia, however, outgrowths are formed from the 
pterygoids and palatines which arch round and meet one 
another ventrally, forming a secondary palate (fig. 43, A), 
which completely shuJ^off the true sphenoidal floor of the 
skull, and c^^Hfeheflpsterior nares which are bounded by 
the pteryg^B BOTL very far back. Though this feature 
is common! ^Btsecondary crocodiles, it is interesting to 

notice that ^B found in the earlier forms, but that its 
gradual evolH ^B be traced. In the Triassic Belodon, for 
instance, the^^^BRor nares open far forwards, and are not 
surrounded by^either the palatines or pterygoids. In the 
Jurassic crocodile, Teleosaurus, the posterior nares lie further 
back, being surrounded by the palatines, but the pterygoids 
do not meet them. Finally, in the Tertiary forms the arrange- 
ments are as in living crocodiles. 

A short secondary hard palate is found also in the Therio- 
dontia. The palatines of Ichthyosaurus are noticeable for their 
transverse position, which recalls that in the Frog. 

The various fossae or vacuities in the false roof of the 
skull are important, and their relations may best be understood 
by a description of their mode of occurrence in Sphenodan, a 
form in which they are very completely developed. 

In Sphenodon, then, on the dorsal surface of the skull, are 
the large supratemporal fossae (fig. 52, 20). Their inner 
margins are separated from one another by the parietal walls 
of the cranium, while externally each is bounded by a bonv 
arch, the supratemporal arcade, formed of the postfrontal, 
post-orbital, and squamosal. Posteriorly the boundary is 



282 



THE VERTEBRATE SKELETON. 




FIG. 52. SKULL OF HATTERIA (Sphenodon punctatus). 
A, lateral; B, dorsal; C, ventral; D, posterior. (After VON ZITTEL.) 



1. premaxilla. 

2. nasal. 

3. prefrontal. 

4. frontal. 

5. postf rental. 

6. parietal. 

7. squamosal. 

8. quadratojugal. 

9. quadrate. 

10. postorbital. 

11. jugal. 

12. maxilla. 

13. vomer. 

14. palatine. 

15. pterygoid. 



16. transpalatine. 

17. exoccipital. 

18. epipterygoid. 

19. basisphenoid. 

20. supratemporal fossa. 

21. infratemporal or lateral tem- 

poral fossa. 

22. orbit. 

23. post-temporal fossa. 

24. foramen magnum. 

25. anterior nares. 

26. interparietal foramen. 

27. dentary. 

28. supra-angular. 

29. articular. 



THE SKELETON IX REPTILES. THE SKULL. 283 

formed by a post-temporal bar, formed by the parietal and 
squamosal. Below the supratemporal arcade is another large 
vacuity, the infra-temporal or lateral temporal fossa (fig. 
52, 21). This is bounded above by the supratemporal arcade, 
and is separated from the orbit in front by the postorbital 
bar, formed by the union of outgrowths from the jugals and 
postorbitals. Behind it is bounded by a continuation of the 
post-temporal bar formed of the squamosal and quadratojugal, 
and below by an infratemporal arcade, which is chiefly com- 
posed of the quadratojugal and jugal. 

Below*^!ie post -temporal bar is a third vacuity, the 
post-temporal fossa (fig. 52, D, 23), bounded above by 
the post-temporal bar and below by the exoccipital and 
opisthotic. 

Sphenodon and the Crocodilia are the only living reptiles 
with complete supratemporal and infratemporal arcades, but 
they are both present in the extinct Pterosauria and some 
Dinosauria. 

Supratemporal fossae, bounded below by supratemporal 
arcades, occur in all reptiles except some Chelonia, the Ophidia, 
the Geckonidae among Lacertilia, and the Pariasauria and 
others among Theromorpha ; they are specially large in X<:>- 
thosaurus among the Sauropterygia, Dicynodon among the 
Theromorpha, and many Crocodilia and Pterosauria. In some 
Dinosaurs, such as Ceratosaurus, they are very small, while 
the infratemporal fossae are correspondingly large. 

In Elginia 1 (Theromorpha) and some Chelonia, such as 
Cltelone, there are no fossae on the surface of the skull, 
a complete false roof being developed ; in other Chelonia, 
such as Trionyx, the true cranium is freely visible, the only 
part of the false roof developed being the infratemporal 
arcade. 

In many reptiles large pre-orbital vacuities occur ; they 

1 E. T. Newton, Phil. Trans, vol. CLXXXIV, B, p. 431 (1893). 



284 THE VERTEBRATE SKELETON. 

are specially large in the Pterosauria and in some of the 
Crocodilia and Dinosauria (fig. 35, 3). In some Pterosauria 
they are confluent with the orbits. 

The premaxillae are usually separate, but sometimes, as in 
some Ophidia (fig. 51, 1), Chelonia, Lacertilia (Agamidae), 
and Dinosaurs (Ceratopsia) they are united. In the Dinosaur 
Hadrosaurus they are exceedingly large and spatulate. In 
the Rhynchocephalian Hyperodapedon they are drawn out into 
a strongly curved beak. 

As regards the mandible, sometimes, as in most Rhyncho- 
cephalia, Ophidia and Pythonomorpha, the rami have only a 
ligamental union ; sometimes, as in Crocodilia, the Rhyncho- 
sauridae and the majority of Lacertilia, they are suturally 
united. In Chelonia (fig. 28, B, 12), and apparently in Ptero- 
sauria, the two dentaries are completely fused together. The 
sutures between the various bones of the lower jaw usually 
persist, but in Ophidia those between the angular, supra - 
angular, articular and coronoid are obliterated. There are 
sometimes large vac.uities in the mandible, as in Theromorpha, 
Crocodilia, and some Dinosauria. In Iguanodon, Polyonaot, 
Hypsilophodon and Hadrosaurus among Dinosaurs the man- 
dible has a predentary or mento-meckelian bone which, in 
some cases at any rate, was probably sheathed in a horny 
beak. 

The principal part of the auditory ossicular chain is formed 
by a rod-like columella. The development of the hyoid appa- 
ratus varies, and it often happens that the first branchial arch 
is better developed than is the hyoid arch. In the Crocodilia 
and Chelonia there is a large basilingual plate or body of the 
hyoid (fig. 53, 1) ; but while in the Crocodilia the first branchial 
forms the only well-developed arch, in the Chelonia the first 
and second branchials are both strongly developed, and the 
hyoid is often fairly large. 



THE SKELETON IX REPTILES. THE RIBS. 



285 



THE RIBS. 

Ribs are always present, and may be attached to any of the 
precaudal vertebrae. In most reptiles the posterior cervical 
vertebrae bear ribs, while the atlas and axis are ribless ; in 
Crocodiles and Geckos, however, ribs are borne even by the 
atlas and axis. On the other hand, in the Chelonia none of 




FIG. 53. HYOIDS OF AS ALLIGATOR (Caiman latirostris) (TO THE LEFT* 
AND OF A GREEN TURTLE (Chelone midas) (TO THE RIGHT) x f. 
(Brit. Mus.> 

The cartilaginous portions are dotted. 

1. basilingual plate or body of 3. first branchial arch (anterior 

the hyoid. cornu). 

2. hyoid arch. 4. second branchial arch (pos- 

terior cornn.) 

the cervical vertebrae bear obvious ribs. In the following 
groups the thoracic ribs have both capitula and tubercula 
Theromorpha, Ichthyosauria, Crocodilia, Dinosauria, Ptero- 
sauria. In the other groups each rib articulates by a single 



286 THE VERTEBRATE SKELETON. 

head, and the position of the facet is subject to a consider- 
able amount of variation, thus in the Squamata it lies on the 
centrum, and in the Sauropterygia on the neural arch, while 
in the Chelonia the rib articulates with the contiguous parts 
of two centra instead of directly with one. 

In most reptiles a greater or smaller number of ribs are 
united ventrally with a sternum ; but in snakes a continuous 
series of similar ribs, all articulating freely with the vertebral 
column, extends from the third cervical vertebra to the end of 
the trunk. The number of ribs connected with the sternum 
varies from three or four in Lizards to eight or nine in Croco- 
diles. Those which reach the sternum are nearly always 
divided into vertebral, sternal, and intermediate portions, and 
as a rule only the vertebral portion is completely ossified. In 
Crocodiles a number of sternal ribs are connected with a 
cartilaginous arch, which is attached to the hind end of the 
sternum, and represents the xiphisternum. The sacral ribs 
connecting the vertebral column with the ilia are very 
distinct in Crocodiles ; in these animals and Sphenodon the 
vertebral ribs have backwardly-projecting uncinate processes 
as in birds. 

In the curious arboreal lizard, Draco volans, the posterior 
ribs are long and straight, and support a parachute-like expan- 
sion of the integument used in its long flight-like leaps. In 
Chelonia the ribs are generally combined with the carapace. 

In Ichthyosauria, Sauropterygia, Crocodilia and Sphenodon, 
abdominal splint ribs occur ; and probably all except the first 
of the paired ossifications forming the plastron of Chelonia are 
of similar character. Abdominal ribs have quite a different 
origin from true ribs, for while true ribs are cartilage bones, 
abdominal ribs have no cartilaginous precursors, but are 
simply the ossified tendons of the rectus abdominalis muscle. 



THE SKELETON IX REPTILES. THE STERNUM. 



287 



THE STERNUM. 

A sternum occurs in the following groups of reptiles : 
Rhynchocephalia, nearly all Lacertilia, Pythonomorpha, Croco- 
dilia, and Pterosauria, and is generally more or less rhomboidal 
or shield-shaped. In Pterosauria it is keeled and bears some 
resemblance to that of birds. It may have been replaced by 
membrane bone. 

The sternum is absent in Sauropterygia, Ichthyosauria, 




FIG. 54. VENTRAL VIEW OF THE SHOULDER-GIRDLE OF STERNUM OF A 
LIZARD (Loemanctus longipes) x2. (After PARKER.) 



1. interclavicle. 

2. clavicle. 

3. scapula. 

4. coracoid. 

5. precoracoidal process. 



6. glenoid cavity. 

7. sternum. 

8. xiphisternum. 

9. sternal rib. 



288 THE VERTEBRATE SKELETON. 

Chelonia, Ophidia, and most of the snake-like Amphisbaenidae 
among Lacertilia ; while it is not well known in Theromorpha 
and Dinosauria. In the Sauropod Brontosaurus, however, two 
rounded bones occur near the base of the coracoids, and these 
probably represent ossified patches in a sternum, which was 
mainly cartilaginous ; similar structures occur in Iguanodon. 

The sternum frequently remains wholly cartilaginous, 
especially in Lacertilia ; sometimes it becomes calcined, but 
true ossification does not as a rule take place. 

APPENDICULAR SKELETON. 

THE PECTORAL GIRDLE. 

The pectoral girdle is well developed in all groups of 
reptiles except the Ophidia, occurring even in the limbless 
Amphisbaenidae. It is very solid in the Theromorpha. As a 
rule all three cartilage bones, scapula, coracoid, and precoracoid 
are represented, and frequently also the membrane bones, 
clavicles, and interclavicle. 

The coracoids are generally flat expanded bones, which 
sometimes, as in Sauropterygia and Ichthyosauria, meet in a 
ventral symphysis ; sometimes, as in Lacertilia, are united with 
the sides of the sternum. In Chelonia neither the coracoids 
nor precoracoids meet one another, but their free ends are 
connected by nbro-cartilaginous bands. In Lacertilia the 
coracoids are pierced by fenestrae. 

The precoracoid is generally represented, but the Thero- 
morpha are the only reptiles in which it is separately ossified; 
it forms a well-marked process on the coracoid in Lacertilia 
(fig. 54, 5). It is absent in Ichthyosauria, and Dinosauria, 
and probably in Sauropterygia. In some Lacertilia and 
Chelonia the sternal ends of the coracoids are unossified and 
form epicoracoids ; in some Chelonia there are also epipre- 
coracoids ; but neither these nor the epicoracoids overlap their 
fellows of the opposite side as they do in arciferous Anura 
(see p. 185). In some Lacertilia with degenerate limbs the 






THE SKELETON IN REPTILES. THE LIMBS. 289 

pectoral girdle is also much reduced, in Ophisaurus apus the 
ventral borders of the coracoids are widely separated. 

A scapula is always present, and is generally expanded 
distally, but in the Chelonia the distal end is cylindrical. In 
the Theromorpha it has an acromial process with which the 
precoracoid articulates, and it is very large in Dinosauria. 
In the Chelonia the scapula and precoracoid are ossified 
continuously. Among the Pterosauria, Pteranodon has an 
unique pectoral girdle; the scapula and coracoid are ankylosed 
and the scapula articulates with the neural spines of several 
ankylosed vertebrae. 

Clavicles occur in some Theromorpha such as Pariasaurus, 
and also in the Ichthyosauria, Sauropterygia, Rhynchocephalia, 
and most Lacertilia. They are absent in the Pterosauria, the 
Chamaeleons among Lacertilia, the Ophidia and the Crocodilia. 
They are wanting too in the Chelonia, unless the first pair of 
ossifications in the plastron are to be regarded as clavicles. In 
the Sauropterygia bones regarded as the clavicles and inter- 
clavicle are generally well developed. The unpaired ossification 
in the plastron of Chelonia is an interclavicle, and a repre- 
sentative of the same bone occurs arising from the sternum in 
Pterosauria. A well developed T-shaped in tercla vide is found 
in Ichthyosauria, Rhynchocephalia, Lacertilia, and some Thero- 
morpha, such as Pariasawrus. 

THE LIMBS. 

In most reptiles there are two pairs of pentedactylate 
limbs provided with claws, but in nearly all Ophidia and 
some Lacertilia (Amp/iisbaena, Lialis, Anguis) the limbs have 
entirely disappeared. In a few Ophidia such as Python traces 
of the posterior limbs occur, and in Chirotes among the Amphis- 
baenidae there are minute anterior limbs. The Lacertilians, 
Chair ides (Seps) and Ophisaurus (Bipes, Pseudopus) have very 
small posterior limbs. 

R. 19 



290 THE VERTEBRATE SKELETON. 

The limbs are as a rule adapted for walking, but in Ichthyo- 
sauria, Sauropterygia, Pythonomorpha and some Chelonia, they 
have the form of swimming paddles, the relative size of the manus 
and pes being increased, while that of the proximal and middle 
portions of the limbs is reduced. This reduction is carried to its 
furthest extent in the Ichthyosauria in which radius and ulna, 
tibia and fibula, have the form of short polygonal bones similar 
to those constituting the manus and pes. In the Pythono- 
morpha the reduction of the limb bones is not quite so marked, 
in the Sauropterygia it is less, and still less in the Chelonia. 
In the earlier Ichthyosauria too, the limb bones are not so 
short as they are in the later forms. The Ichthyosaurian limb 
is also remarkable, firstly for the fact that both humerus and 
femur are terminated by concave articulating surfaces instead 
of by convex condyles, and secondly for the great multiplication 
of the phalangeal bones, each digit being sometimes composed of 
a series of over twenty. Sometimes too the number of series is 
increased, either by the bifurcation of some of the digits or by 
the development of marginal bones. In the Sauropterygia the 
phalanges are likewise increased above the normal but not so 
much as in Ichthyosauria. The humerus and femur of Sauro- 
pterygia are noticeable for the enormous size of the terminal 
epiphyses which form in each case by far the greater part of 
the bone. 

THE ANTERIOR LIMB. 

The anterior limb is usually approximately equal in 
length to the posterior, but in many Dinosauria it is consider- 
ably the shorter of the two. The humerus is generally with- 
out distinct condyles, but they are well developed in the Thero- 
morpha, the Lacertilia and Sphenodon. 

In the Theroniorpha, some Rhynchocephalia, and some 
Sauropterygia, such as Mesosaurus, the humerus has an ent-epi- 
condylar foramen ; in Lacertilia, Chelonia and some Dinosauria 
there is an ect-epicondylar foramen or groove ; Sphenodon 



THE SKELETON IX REPTILES. PELVIC GIRDLE. 291 

possesses both ent- and ect-epicondylar foramina. The radius 
and ulna are always separate. In some Chelonia, such as 
Chetydra, the carpus has a very simple arrangement, namely, 
a proximal row of three bones, the radiale, intermedium and 
ulnare, and a distal row of five carpah'a, with one bone, the 
centrale, between the two rows. Many reptiles have a carpus 
only slightly different from this. Thus the carpus in Spheno- 
'don differs mainly in having two centralia, that of most Lacer- 
tilia, in having the centrale and intermedium fused. 

Crocodiles have a much reduced carpus with the radiale 
and ulnare considerably elongated. The manus in Chamaeleons 
is curiously modified, having the first three digits arranged in 
one group and turned inwards, and the fourth and fifth in 
another group turned outwards ; carpalia 3 and 4 are united. 

In the Pterosauria the anterior limbs form wings, the 
phalanges of the fifth digit being very greatly elongated to 
support the wing membrane. The first digit is vestigial and 
the second, third, and fourth are clawed. 

THE PELVIC GIRDLE. 

The pelvic girdle is well developed in all reptiles which 
have posterior limbs, but is absent or quite vestigial in Ophidia 
and those Lacertilia which have no posterior limbs. The ilium 
and ischium agree in their general characters throughout all 
the various groups of reptiles, but that is not the case with 
the pubis. 

In many reptiles such as Chelonia, Ichthyosauria and 
Lacertilia the ilia are small, more or less cylindrical bones 
either directed backwards, or vertically placed as in the 
Chamaeleons. In the Crocodilia they are larger and more ex- 
panded, while in Dinosauria and Pterosauria they are greatlv 
elongated both in front of, and behind, the acetabulum. The 
ischia are generally strongly developed somewhat square bones 
meeting in a ventral symphysis. In Dinosauria the ischium 
(fig. 35, 9) is a much elongated and backwardly-directed bone, 

192 



292 THE VERTEBRATE SKELETON. 

bearing a forwardly projecting obturator process. In Ptero- 
sauria the ischium is fused with the ilium, and in both ptero- 
saurs and crocodiles the ilium and ischiuin are the only bones 
taking part in the formation of the acetabulum. In most 
Lacertilia there is an unpaired structure, the hypo-ischium or 
os cloacae projecting back from the symphysis ischii, which is 
usually separated from the symphysis pubis by a large space, 
the foramen cordiforme. In some Lacertilia and Chelonia 
there is a cartilaginous bar dividing the foramen cordiforme 
into two obturator foramina; in many Chelonia this bar is 
ossified. Among Ophidia, Python, Tortrix, Typhlops and their 
allies have a structure representing a vestigial ischio-pubis : 
but in most Ophidia there is no trace of the pelvis. In some 
Theromorpha all the bones of the pelvis are completely fused, 
forming an os innominatum as in mammals ; the pubes and 
ischia are so completely fused that sometimes as in Paria- 
saums even the obturator foramina are closed. 

Concerning the reptilian pubis there are considerable diffi- 
culties. Sometimes there is only a single pubic structure 
present, sometimes there are two. The reptilian pubis is best 
understood by comparing the arrangements met with in the 
various other groups with that in the Orthopod Dinosaurs 
such as Iguanodon. In Iguanodon the pubis consists of two 
portions, viz. of a moderately broad pre-pubis directed down- 
wards and forwards, and of a narrow greatly elongated post- 
pubis directed backwards parallel to the ischium. The pubis 
is united to both ilium and ischium, the acetabulum has a 
large unossified space, and neither pre-pubes nor post-pubes 
meet in ventral symphyses. The arrangement bears a great 
resemblance to that of Ratite birds. In Lacertilia, Chelonia, 
Rhynchocephalia and Ichthyosauria together with Theropod 
and Sauropod Dinosaurs the pubis corresponds to the pre-pubis 
of Iguanodon and is a more or less cylindrical bone expanded 
at both ends, meeting its fellow in a ventral symphysis. In 
Chelonia and Lacertilia the pubis bears a lateral process which 



THE SKELETON IX REFITLES. POSTERIOR LIMB. 293 

is homologous with the post-pubis of Iguanodon. In Lacer- 
tilia and sometimes in Chelonia there is a cartilaginous epipubis 
attached to the anterior border of the pubic svmphvsis ; this is 
well developed in the Chamaeleons and Geckos. In Crocodilia 
there is, forming the anterior and ventral portion of the 
acetabulum, a patch of cartilage (fig. 49, 3) which is probably 
the true pubis homologous with that of lizards and with the 
pre-pubis of Iguanodon. The large bone generally called the 
pubis in Crocodiles is probably an epipubis. 

THE POSTERIOR LIMB. 

The posterior limb is entirely absent in some Lacertilia and 
in most Ophidia, though traces occur in Python, Tortrix and 
Ti/phlops. In the Ichthyosauria, Sauropterygia and Pythono- 
morpha the posterior limbs form swimming paddles and have 
been already referred to. 

The arrangement of the proximal and middle segments of 
the limb is fairly constant in all reptiles with limbs adapted 
for walking, and the tibia and fibula are always separate. 
The pes is however subject to a considerable amount of varia- 
tion, especially as regards the tarsus. In some Chelonia the 
tarsus like the carpus has an extremely simple arrangement, 
consisting of a proximal row of three bones, the tibiale, inter- 
medium and fibulare, a centrale, and a distal row of five tar- 
salia. In most living reptiles, however, the tibiale and inter- 
medium are as in mammals united, forming the astragalus. 
In Crocodiles (fig. 48, B, 15) the centrale is also united with 
the tibiale while the distal tarsalia are very slightly developed. 
The calcaneum in Crocodiles is drawn out into a long process 
forming a heel in a manner almost unique among Sauropsida. 
In Sphenodon and Lacertilia the tibia and fibula articulate 
with a single large bone representing the whole proximal row 
of tarsalia. 

The pes is generally pentedactylate, but in some Crocodiles 
the fifth digit is vestigial (fig. 48, B), and in some Dinosauria 



294 THE VERTEBRATE SKELETON. 

(fig. 35) there are only three digits. The North American Dino- 
saurs present a continuous series ranging from a pentedactylate 
plantigrade form like Morosaurus, to such a form as JJallopus 
with a highly digitigrade and specialised pes reduced to three 
functional digits, and a vestigial fifth metatarsal. The second, 
third and fourth metatarsals in this form are nearly two- 
thirds as long as the femur, and the calcaneum is drawn out 
into a heel much as it is in most mammals. 

In Lacertilia, Orthopoda and many Chelonia, the ankle 
joint comes to lie between the proximal and distal row of 
tarsals as in birds. 






CHAPTER XVII. 

CLASS. AVES 1 . 

BIRDS form a large and extremely homogeneous class of the 
vertebrata, and are readily distinguished from all other animals 
by the possession of an epidermal exoskeleton having the form 
of feathers. Feathers differ from hairs in the fact that they 
grow from papillae formed of both the horny and the Mal- 
pighian layer of the epidermis, which papillae at first project 
from the surface, and only subsequently become imbedded in 
pits of the dermis. A dermal exoskeleton does not occur in 
birds. 

The endoskeleton is characterised by its lightness, the 
large bones being generally hollow ; but the pneumaticity 
does not vary in proportion to the power of night. The 
cervical part of the vertebral column is very long and flexible, 
while the postcervical portion is generally very rigid, owing 
to the fusion of many of the vertebrae, especially in the 
lumbar and sacral regions. The vertebrae are generally with- 
out epiphyses to their centra. The cervical vertebrae in living 
forms have saddle-shaped articulating surfaces, and many of 
them bear ribs. The thoracic ribs in almost all birds have 
large uncinate processes. The sternum is very large, and the 
ribs are always attached to its sides, not as in many reptiles 

1 M. Fiirbringer, Untersuchungen zur Morphologic und Systematik der 
I'ogel, I. and II. Amsterdam, 1888. Cf. H. Gadow, Nature, xxxix. 
1888, pp. 150 and 177. 

T. H. Huxley, "On the classification of birds." P. Z. S., London, 
1867. 

E. Selenka and H. Gadow, V'dgel in Bronn's Classen und Ordnungen 
des Thier-reichs 18691890. 



296 THE VERTEBRATE SKELETON. 

to any backwardly-projecting process or processes. The sternum 
ossifies from two or more centres. 

The skull is extremely light, and its component bones show 
a great tendency to fuse together completely. The facial part 
of the skull is prolonged into a beak, chiefly formed of the pre- 
maxillae ; this beak is in all modern birds devoid of teeth, 
and is coated externally with a horny epidermal sheath. The 
quadrate is large and freely movable. The supratemporal 
arcade 1 is imperfect, while the infratemporal arcade 1 is com- 
plete. There are no postorbital or postfrontal bones. Neither 
parotic processes nor an interparietal foramen occur. There 
are commonly large pre-orbital vacuities. The palatines 
and pterygoids never form a secondary bony palate as in 
Crocodiles. Part of the floor of the skull is formed by a 
wide basitemporal (paired in the embryo) which is continued 
in front as a long slender rostrum ; these structures have re- 
placed the paraspheuoid of Ichthyopsids. Cartilage or bone is 
always developed in the sclerotic. The first branchial arch is 
well developed, the hyoid arch but slightly. The coracoids 
are large, and the clavicles are nearly always united forming 
ihefurcula. There is no separate interclavicle and hardly any 
trace of a precoracoid. 

The anterior limbs form wings, and the manus is in the 
adult always much modified, never having more than three 
digits. The three bones of the pelvis are, except in Archaeor- 
nithes, always ankylosed together in the adult, and the ilium 
is greatly prolonged in front of the acetabulum, which is 
perforated. The ilia are not connected with the sacrum by 
ossified sacral ribs. The pubes and ischia are directed back- 
wards parallel to one another, and except in a very few forms 
never meet their fellows in ventral symphyses. The fibula 
is generally much reduced. The proximal tarsal bones are 
always ankylosed to the tibia, and the distal tarsals to the 
metatarsals, so that the ankle joint is intertarsal. The first 
1 See p. 283. 



AYES. ARCHAEORNITHES. 297 

metatarsal is nearly always free. The pes never has more than 
four digits in the adult. 

The class Aves is most conveniently divided into two sub- 
classes : 1. Archaeornithes. 2. Xeornithes. 

Subclass I. ARCHAEORXITHES. 

The only form referred to this subclass of extinct birds is 
Archaeoptwyx 1 , the earliest known bird. In this animal the 
skeleton does not seem to be pneumatic. The cervical and 
trunk vertebrae are generally thought to be flat, certainly 
their articulating surfaces are not saddle-shaped. There is no 
long compound sacrum as in modern birds. The tail is longer 
than the whole body, the caudal vertebrae are twenty in 
number, they gradually taper as traced away from the trunk, 
and each bears a pair of feathers. The posterior caudal 
vertebrae are not united together to form a pygostyle. The 
upper jaw bears thirteen pairs of conical teeth, planted in 
distinct sockets in the maxillae and premaxillae, but the 
mandible has only three pairs. The presence of these teeth 
forms the most essential difference between the skull of 
Archaeopteryx and that of modern birds, and the fact that 
they occur on the premaxillae renders it improbable that 
a horny beak was present. There is a ring of ossifications 
in the sclerotic. The ribs do not show uncinate processes, 
and articulate with the vertebrae by single heads not divided 
into capitula and tubercula. Abdominal ribs appear to have 
been present. The f urcula is large, and the scapula has a well 
developed acromion. The sternum is unknown. The radius 
and ulna are approximately equal in size. In the manus the 
first, second and third digits 2 are present, each terminated by 

1 B. Owen, Phil. Trans., vol. cxin., p. 33; 1863. T. H. Huxley, 
P. E. S., vol. XTI., p. 243; 1868. C. Vogt, Rev. Scient., ser. 2, torn. 9, 
p. 241; 1879. C. H. Hurst, Xat. Set., voL in., p. 275; 1893; vol. vi., 
pp. 112, 180, 244; 1895. W. P. Pycraft, Xat. Set., vol. v., pp. 350 and 
437; 1894; and vol. vin., p. 261; 1896. 

- According to Hurst the fourth and fifth digits are also present. 



298 THE VERTEBRATE SKELETON. 

a claw. The second digit is considerably the longest, while 
the third includes four phalanges. The three bones of the 
pelvis probably remained distinct throughout life. The tarsals 
are ankylosed respectively to the tibia and metatarsals as in 
other birds. The metatarsals are ankylosed together, and the 
pes has four digits. 

Subclass II. NEORNITHES. 

To this subclass may be referred all known birds except 
Archaeopteryx. They all agree in having a short tail whose 
component vertebrae are commonly ankylosed together form- 
ing a pygostyle. The three metacarpals do not all remain 
distinct. The bones of the pelvis are ankylosed together, 
and to a large though variable number of vertebrae. There 
are three orders, the Ratitae, Oclontolcae, and Carinatae. 

Order 1. RATITAE. 

The Ratitae differ from Archaeopteryx and the great 
majority of Carinatae in being flightless. The bones are 
generally not pneumatic, containing marrow instead of air, 
in the Ostrich however they are very pneumatic. The tail 
is short and the posterior caudal vertebrae are generally 
ankylosed together forming a pygostyle. The pectoral girdle 
has comparatively a much smaller size than in Carinatae, 
clavicles are small or absent, and the scapula and coracoid 
lie nearly in the same straight line. The ilium and ischium 
do not as in Carinatae unite posteriorly, and enclose a 
foramen except in very old Rheas and Emeus. The quadrate 
articulates with the cranium by a single head. The vomers 
unite and form a broad plate, separating the palatines, ptery- 
goids and basisphenoidal rostrum. 

The anterior limbs are greatly reduced in size or even 
absent, while the posterior limbs are greatly developed and 
adapted for running. The tibia and fibula are quite distinct. 



AYES. RATITAE. 299 

Many ornithologists agree that the various forms grouped 
together as Katitae are not all very closely allied to one another, 
that they resemble one another mainly in having lost the power 
of flight, and do not form a natural group. 

The Ratitae include the following groups : 

^EpyornitJies 1 , huge extinct birds from Madagascar. 

Apteryges, including the Apteryx of New Zealand. 

Dinornithes*, the Moas, huge extinct birds from New 
Zealand, and some of the neighbouring islands. 

Megistanes, including the Cassowaries (Cas^^arius) of Aus- 
tralia, New Guinea, and some of the neighbouring islands ; 
and the Emeus (Dromapus) of Australia. 

Rheornithes, including the Rheas of S. America. 

Stnttkwrnithety including the Ostriches (Struthio) now living 
in Africa, and found fossil in N. India and Samos. 

Order 2. ODONTOLCAE. 

This order includes only an extinct N. American bird 
Hesperornis*. The jaws are provided with a series of sharp 
teeth placed in continuous grooves, but the premaxillae are 
toothless, and were probably sheathed in a horny beak. The 
rarni of the mandible are not ankylosed together in front. 
The skeleton is not pneumatic. The cervical vertebrae have 
saddle-shaped articulating surfaces as in ordinary birds, and 
the thoracic vertebrae are not ankylosed together. The tail 
is comparatively long, and formed of twelve vertebrae with 
only slight indications of a pygostyle. The ribs have uncinate 
processes. The anterior limb is quite vestigial, being reduced 
to a slender humerus. The posterior limb is very powerful 
and adapted for swimming. 

1 See C. W. Andrews, P. Z. S., 1894, p. 108. 

- See T. J. Parker, 2V. Zool. Soc. London, vol. xiu., pt. 2, 1895, and 
F. W. Button, several papers in Tr. N. Zealand Inst., 1893 and 1895. 

3 See O. C. Marsh. Odontornithes. A monograph of the extinct toothed 
birds of X. America. Nevrhaven, 1880. 



300 THE VERTEBRATE SKELETON. 

Order 3. CARINATAE. 

This order includes the vast majority of living birds. 
The cervical vertebrae have saddle-shaped articulating surfaces 
(except in the Ichthyornithiformes). The posterior caudal 
vertebrae are ankylosed forming a pygostyle. The quadrate 
articulates with the cranium by a double head. In all except 
the Tinamidae the vomers are narrow behind and not inter- 
posed between the palatines, pterygoids and basisphenoidal 
rostrum. The sternum has a median keel, and the anterior 
limbs are in the great majority of cases adapted for flight. 
Clavicles are well developed, and the scapula and coracoid are 
nearly at right angles to one another. The various groups 
into which the Carinatae are divisible are shown in the table 
on pp. 40 42. Their special characters will not be dealt with. 

FIG. 55. Gallus bankiva var. domesticits. THE LEFT HALF OF THE SKELETON. 
The skull, vertebral column, and sternum are bisected in the median 
plane. (After Marshall and Hurst.) 

A, acetabulum. B, cerebral fossa. CB, cerebellar fossa. CL, clavicle. CO, coracoid. 
CR, cervical rib. C l = one, first cervical vertebra. FE, femur. HC, ventral end of clavicle. 
IIU, humerus. IIY, liyoid. IF, ilio-sciatic foramen. IL, ilium. IS, ischium. L, lachrymal. 
MC 3, postaxial metacarpal. MN, mandible. MS, xiphoid processes. MT, tarso-metatarsus. 
MT 1, first metatarsal. N, nasal. OP, optic foramen. P, premaxilla. PB, pubis. PL, 
palatine. PY, pygostyle. R, radius. RC, radial carpal. S, keel of sternum. SC, scapula. 
T, tibio-tarsus. TH 4, fourth thoracic vertebra. U, ulna. UC, ulnar carpal. UP, uncinate 
process. Z, infra-orbital bar. 1, 2, 3, 4, first, second, third and fourth digits of pes. 3, pre- 
axial, 4, middle, and 5, postaxial digit of manus. 



AVES. CARIXATAE. 



301 




FIG. 55. 



CHAPTER XVIII. 

THE SKELETON OF THE WILD DUCK (Anas 
boschas). 

I. EXOSKELETOK 

The exoskeleton of the Duck and indeed of all birds is 
entirely epidermal in origin. Its most important part consists 
of feathers, but it includes also the following horny struc- 
tures : 

(a) scales, which cover the toes and tarso-metatarsus ; 

(6) claws, which are attached to the distal phalanges of 
the toes arid of the pollex ; 

(c) the wide beak, which sheaths both upper and lower 
jaws, and whose edges are raised into lamellae, which act as 
strainers. 

FEATHERS. 

A well developed feather, such as one of the large 
quill feathers of the wing or tail, consists of the following 
parts: A main stem, the scapus, which forms the axis 
running along the whole length of the feather, and is divided 
into (1) a proximal hollow cylindrical portion, the calamus or 
quill, and (2) a distal solid portion, the rachis or shaft, which 
is square in section, flexible and grooved along its ventral 
surface, and bears a number of lateral processes, the barbs. 
The calamus which is partly imbedded in a pit in the dermis, 



SKELETON OF THE WILD DUCK. THE FEATHERS. 303 

bears two holes : one, the inferior umbilicus, is at its 
proximal end, and into it enters a vascular outgrowth from the 
derruis; the other, the superior umbilicus, lies on the 
ventral surface at the junction of the calamus and scapus. 

The barbs are a series of narrow elastic plates, attached 
by their bases to the rachis, and with their edges looking 
upwards and downwards. The barbs are connected together 
by a number of smaller processes, the barbules, which inter- 
lock with one another by means of booklets, and bear the 
same relation to the barbs that the barbs do to the rachis. 
The barbs and barbules, together with the rachis, constitute 
the vexillum or vane of the feather. Any feather having 
the above type of structure is called a penna or a contour 
feather, from the fact that it helps to produce the contour of 
the body. 

VARIETIES OF FEATHERS. 

1. Pennae. There are two kinds of pennae or contour 
feathers. 

(a) The quills. These form the large feathers of the 
wing and tail. They are divided into two groups, the 
remiges, or wing quills, and the rectrices, or tail quills. 

The remiges 1 include three sets of feathers, the primaries 
or metacarpo-digitals, which are attached to the bones of 
the manus, the secondaries or cubitals, which are attached 
to the ulna, and the numerals, which are attached to the 
humerus. 

The primaries differ from all the other quill feathers 
in having the posterior half of the vane much wider than the 
anterior half. They are ten in number, and of these six, 
the metacarpal quills (fig. 57, 14), are attached to the second 
and third metacarpals, one, the ad-digital (fig. 57, 15), to the 
phalanx of the third digit, two. the mid-digitals (fig. 57, 16). 
to the first phalanx of the second digit, and two, the pre-digitals 

1 See B. S. Wray, P. Z. S., 1887, p. 343. 



304 



THE VERTEBRATE SKELETON. 



(fig. 51, 17), to the second phalanx of the second digit. One 
of the pre-digitals is very small, and is called the remicle 
(fig. 57, 11). 




FIG. 56. THE WING OF A WILD DUCK (Anas boschax). 

The upper figure shows the dorsal side of a right wing, the lower figure 

the ventral side of a left wing, x \. (Brit. Mus.) 

1. scapulars. 6. metacarpo-digitals or pri- 

2. tectrices marginales. maries. 

3. tectrices minores. 7. tectrices mediae. 

4. bastard wing. 8. cubitals or secondaries. 

5. tectrices majores. 9. pennae humerales. 

10. pennae axillares. 

In addition, a group of three quill feathers is attached to 
the first digit, constituting the bastard wing or ala spuria 
(fig. 56, 4). 

The secondaries or cubitals (tig. 56, 8) form a group of 
seventeen feathers, attached to the ulna ; they are shorter than 



SKELETON OF THE WILD DUCK. THE FEATHERS. 305 

the primaries, and do not have the posterior half of the vane 
much wider than the anterior half. 

The humerals (figs. 56, 9 and 57, 12) form a group of 
eight small feathers, of varying length, attached to the anterior 
half of the humerus. 




B 



FIG. 57. WINGS OF A WILD DUCK WITH THE COVERTS REMOVEI> 

(Anas boschas). x-J. 

A. Bight wing seen from the dorsal side. B. Left wing disarticulated 
and seen from the ventral side. (Brit. Mas.) 



1. humerus. 

2. radius. 

3. ulna. 

4. radial carpal. 

5. ulnar carpal. 

6. first phalanx of first digit. 

7. second metacarpal. 

8. third metacarpal. 

9. first phalanx of second digit. 

R. 



10. second phalanx of second 

digit. 

11. remicle. 

12. pennae humerales. 

13. cubitals or secondaries. 

14. metacarpal quills. 

15. ad-digital. 

16. mid-digitals. 

17. pre-digital. 

-20 



306 THE VERTEBRATE SKELETON. 

(b) The tectrices or coverts are short feathers, which 
cover over the quills of the rectrices and remiges, and clothe 
the body generally. Their barbules are less developed than is 
the case with the quill feathers, so that the barbs separate 
readily from one another, especially at the base of the vane. 
The nomenclature of the various patches of coverts on the 
wings is seen in fig. 56. A small patch of backwardly -directed 
feathers surrounding the external auditory opening are known 
as the auriculars. 

2. The filoplumes are rudimentary feathers, consisting 
of a minute stem and slightly developed vane. They are left 
in the skin after the other feathers have been removed. 

3. The plumulae, or down feathers, have the stem very 
slightly developed, while the barbs are soft and free from one 
another. They are distributed all over the body, not only 
among the contour feathers, but also over the spaces (apteria) 
which bear no contour feathers. 

In the young bird the rudiments of the new feathers are 
formed at the bases of the embryonic down feathers, and as 
they grow they push them out from the skin. The embryonic 
down feathers however remain attached to the apices of the 
new feathers till these have reached a length of about an 
inch ; they are then shed. 

II. ENDOSKELETON. 

As compared with that of the Turtle or Crocodile, the 
endoskeleton of the Duck is characterised by : 

1. The great lightness of the bones, many of which con- 
tain air cavities. 

2. The tendency to become ankylosed together shown by 
many of the bones. 

3. The modification of the anterior limbs and girdle for 
the purpose of flight. 



SKELETON OF THE WILD DUCK. VERTEBRAL COLUMN. 307 

1. THE AXIAL SKELETON. 

This, as in other vertebrates, is divisible into 

A. The vertebral column. 

B. The skull. 

C. The ribs and sternum. 

A. THE VERTEBRAL COLUMN. 

The vertebral column of the duck, like that of the great 
majority of birds, presents a number of well-marked character- 
istics, contrasting strongly with those of the generality of 
higher vertebrates. The centra are always without epiphyses. 
The neck is exceedingly long, about as long as all the rest of 
the vertebral column put together, and is remarkable for its 
flexibility. The trunk portion of the vertebral column on the 
other hand is characterised by extreme rigidity, and the 
marked tendency shown by the component vertebrae to fuse 
together into one almost continuous mass. The most rigid 
part of the vertebral column is that to which the pelvis is 
united, as no less than seventeen vertebrae take part in the 
union. The tail of the duck, like that of all living birds, is 
very short, and the posterior caudal vertebrae are united 
togther, forming the pygostyle. The vertebral column may 
be divided into cervical, thoracic, lumbar, sacral, and caudal 
regions, but the boundaries between the several regions are ill- 
defined. 

THE CERVICAL VERTEBRAE. 

All the vertebrae anterior to the first one that bears a rib 
meeting the sternum are regarded as cervical vertebrae. 
There are therefore sixteen cervical vertebrae, the last two of 
which bear well developed ribs. All are freely movable on 
one another. 

As a typical cervical vertebrae, any one from the fifth to 
the ninth may be taken. The vertebra is rather elongated, 
and is very lightly and strongly made, its most characteristic 

202 



308 THE VERTEBRATE SKELETON. 

feature being the shape of the articulating surfaces of the 
centra, which are generally described as saddle-shaped. The 
anterior surface is convex from above downward, and concave 
from side to side, while the posterior and more prominent 
surface is concave from above downwards and convex from 
side to side. The neural arch is low, and is drawn out into a 
slight blade-like neural spine. Its base is deeply notched on 
both sides posteriorly for the exit of the spinal nerves. Above 
these notches it is drawn out into two rather prominent 
diverging processes, which bear the postzygapophyses, 
two flattened surfaces which look downwards and outwards. 
The transverse processes form irregular outgrowths from 
the anterior two-thirds of the sides of the vertebra ; each 
projects for a short distance downwards and outwards, and 
is terminated posteriorly by a short backwardly-projecting 
spine. The transverse processes are shown by development 
to ossify from separate centres, and are therefore to be 
regarded as cervical ribs, and each is perforated at its base by 
a canal for the passage of the vertebral artery. Above the 
anterior end of the vertebrarterial canal are a pair of 
thickened outgrowths, which bear upwardly and inwardly 
directed prezygapophyses. Each transverse process is 
perforated near its middle by a prominent foramen through 
which passes a vein which is connected with the jugular vein. 
The third and fourth cervical vertebrae resemble the suc- 
ceeding ones in most respects, but have small hypapophyses, 
and the neural spines are less blade-like. The posterior 
cervical vertebrae (tenth to sixteenth) differ somewhat from 
the middle ones. They are shorter and more massive, tin' 
neural arch is much shorter, being deeply notched in the 
middle line in front and behind. The transverse processes arise 
from the anterior half of the vertebra only, and in the eleventh 
vertebra each is drawn out below into a pair of rather promi- 
nent downwardly and inwardly directed processes. In the 
twelfth vertebra these processes have almost coalesced, and 



SKELETON OF THE WILD DUCK. VERTEBRAL COLUMN. 309 

in the thirteenth vertebra they have coalesced completely, 
forming a prominent hypapophysis. In the succeeding 
vertebrae this hypapophysis rapidly decreases in size. 

The fifteenth and sixteenth cervical vertebrae resemble the 
succeeding thoracic vertebrae, having short thick centra and 
prominent squarely truncated neural spines ; the sides of the 
neural arches are very deeply notched. The fifteenth vertebra 
has a short transverse process, perforated by a wide vertebrar- 
terial foramen, but this foramen is absent in the sixteenth. 
The transverse processes of the fifteenth vertebra bear two 
facets for the articulation of the capitulum and tuberculum of 
the rib. The sixteenth vertebra has its tubercular facet on 
the transverse process, but the capitular facet is borne on the 
centrum. 

The second or axis vertebra is small, and has the centrum 
drawn out into a comparatively very large hypapophysis. The 
posterior articulating surface of the centrum is saddle-shaped, 
the anterior nearly flat : above it the centrum is prolonged 
into the prominent odontoid process, which is shown by 
development to be the detached centrum of the atlas. The 
neural arch is deeply notched in the middle line in front, and 
at the sides behind. It is drawn out posteriorly into a wide 
massive outgrowth, which overhangs the third vertebra and 
bears the downwardly-directed postzygapophyses. The pre- 
zygapophyses are situated at the sides of the anterior end of 
the neural arch, and look directly outwards. The transverse 
processes are very slightly developed, and are pierced by the 
vertebrarterial canals. 

The atlas vertebra is a very slight ring-like structure, 
thickened ventrally and bearing in front a prominent concave 
cavity for articulation with the occipital condyle of the skull. 
Posteriorly it bears a more or less flattened surface for arti- 
culation with the centrum of the axis. It surrounds a large 
cavity partially divided into a larger dorsal portion, which is 
the neural canal, and a smaller ventral portion which lodges 



310 THE VERTEBRATE SKELETON. 

the odontoid process. The sides of the atlas are pierced by 
the vertebra rterial canals, above which there are two slight 
backwardly-projecting outgrowths bearing the postzygapophyses 
on their inner faces. 

THE THORACIC VERTEBRAE. 

The thoracic region includes all the vertebrae bearing free 
ribs, except the first two, viz. those whose ribs do not reach 
the sternum. There are seven thoracic vertebrae. The first 
four have centra with saddle-shaped articulating surfaces, but 
are more or less firmly united together by their neural spines ; 
the last two are completely ankylosed by their centra to the 
lumbar vertebrae. 

Each of the first five vertebrae has a prominent, vertical, 
abruptly terminated neural spine, and straight transverse 
processes. The zygapophyses and articulating surfaces at the 
ends of the centra are well developed. The third, fourth, fifth, 
and sixth vertebrae have very prominent hypapophyses. The 
articular facets for the ribs are well marked, those for the tu- 
bercula lying at the free ends of the transverse processes, and 
those for the capitula at the sides of the anterior ends of the 
centra. The sixth and seventh thoracic vertebrae are firmly 
fused by their centra and neural arches to one another and 
to the lumbar vertebrae behind, and by their transverse pro- 
cesses to the ilia. The sixth has its centrum terminated in 
front by a saddle-shaped articulating surface, and bears a pair 
of prominent prezygapophyses. Its transverse processes and 
centrum bear facets for the tubercula and capitula of the ribs 
respectively. In the seventh vertebra the tubercular facet is 
wanting. 

THE SACRUM. 

The sacrum generally consists of seventeen vertebrae 
fused with one another and with the ilia. Their number may 
be reckoned from the number of foramina for the exit of spinal 
nerves. The two most anterior of these vertebrae bear 



SKELETON OF THE WILD DUCK. THE SACRUM. 31 1 



and have been already described with the other thoracic 
vertebrae. Their neural spines and those of the four succeed- 
ing vertebrae are fused together, forming a continuous crest 
of bone completely united laterally with the ilia. The trans- 
verse processes of all these six vertebrae are well developed, 




FlG. 58. A, DORSAL AND B, VENTRAL VIEW OF THE PELVIS AND SACRUM OF 

A DUCK (Anas boscha*). 

1. ilium. 4. pectineal process. 

2. ischium. 5. lumbar vertebrae. 

3. pubis. 6. true sacral vertebrae. 

but those of the posterior two (fig. 58, B, 5) are much the 
stoutest. The next three vertebrae have broad centra, but 
their transverse processes are very slightly developed and have 
no ventral elements. These seven vertebrae belong to the 
lumbar series. The remaining eight vertebrae have well- 
developed transverse processes, which in the case of the first 
three or four are divisible into dorsal and ventral elements. 
All the dorsal elements are united to form a pair of flattened 
plates, partially separated by a series of foramina from a 



312 



THE VERTEBRATE SKELETON. 



median plate formed by the united neural arches. Laterally 
they are continuous with the ischia. The first two of this 
series of vertebrae are shown by their relation to the nerves 
to be the true sacrals (fig. 58, B, 6), the remaining six belong- 
ing to the caudal series. 

Behind them come the six free caudal vertebrae, succeeded 
by a terminal piece, the pygostyle, formed of a number of 
vertebrae fused together ; this bears the rectrices or tail quills. 



18,. 




FIG. 59. SKULL OF A DUCK (Anas boschas). x 1. 
A. Dorsal view of the cranium. B. Palatal view of the mandible. 

C. The Hyoid. 
For numbers see Fig. 60. 

B. THE SKULL. 

The skull of the duck, like that of birds in general, is 
characterised (1) by its lightness, (2) by the contrast between 



SKELETON OF THE WILD DUCK. THE SKULL. 313 

11 
A oo IP 



22 



29 




18 14 

FIG. 60. A. Ventral view of the cranium of a Duck (Anas boschas). 
B. Cranium and mandible seen from the left side, x 1. 



1. maxilla. 

2. premaxilla. 

3. anterior nares. 

4. nasal process of premaxilla 

(fig- 59). 

5. nasal. 

6. frontal (fig. 59). 

7. lachrymal. 

8. postfrontal process. 

9. parietal (fig. 59). 

10. jugal. 

11. quadra tojugal. 

12. quadrate. 

13. condyle of mandible. 

14. posterior articular process. 

15. dentary at symphysis. ' 

16. basi-hyal. (fig. 

17. uro-hyaL 59). 

18. basibranckial. 

19. vomer. 

20. palatine. 

21. pterygoid. 



22. anterior palatine foramen. 

23. basitemporal. 

24. foramen leading into tympanic 

cavity. 

25. bristle inserted into posterior 

opening of carotid canal. 

26. bristle inserted into posterior 

opening of Eustachian 
canal. 

27. bristle emerging through an- 

terior opening of carotid 
canal. Close by is seen the 
bristle emerging through 
the anterior opening of the 
Eustachian canal. 

28. fenestral recess. 

29. maxillo-palatine. 

30. lambdoidal crest. 

31. rostrum. 

I. II. IV. V. IX. X. nerve fora- 
mina. 



314 THE VERTEBRATE SKELETON. 

the bones of the cranium proper and those forming the '-rest 
of the skull, for the bones forming the cranium proper are 
closely fused together, the sutures between them being nearly 
all completely obliterated in the adult, while the bones form- 
ing the face are loosely connected with the cranium proper ; 

(3) by the prolongation of the face into a long toothless beak ; 

(4) by the size of the orbits, and their position entirely in 
front of the cranium, so that they are separated from one 
another only by a thin interorbital septum. 

For purposes of description the skull may be divided into 

(1) The cranial portion. 

(2) The facial portion. 

(3) The mandible. 

(4) The hyoid. 

(1) THE CRANIAL PORTION. 

This is a rounded box expanded dorsally and posteriorly, 
but tapering antero-ventrally. In the young skull the divi- 
sional lines between the several bones can be easily seen, 
but in the adult they are quite obliterated. 

(a) The dorsal surface is rounded, expanded in front and 
behind, but encroached upon in the middle by the cavities of the 
orbits. There is a prominent divisional line in front, separating 
it from the facial part of the skull. It is formed mainly by 
the frontal (fig. 59, A, 6) and parietal bones, but the frontals 
diverge a little anteriorly and enclose between them the ends 
of the nasal processes (fig. 59, A, 4) of the premaxillae. Just 
in front of the orbit the outer margins of the frontals are 
either notched or pierced by a pair of foramina. 

(b) At the posterior end of the cranium the most promi- 
nent feature is the large, almost circular foramen magnum, 
through which the spinal cord and brain communicate ; this in 
young birds is seen to be bounded by four distinct bones, dor- 
sally by the supra-occipital, ventrally by the basi-occipital, 
and laterally by the exoccipitals. 



SKELETON OF THE WILD DUCK. THE SKULL. 315 

The basi-occipital forms the main part of a prominent 
convex knob, the occipital condyle, with which the atlas 
articulates. The occipital condyle is slightly notched above, 
and the ventral surface of the cranium is deeply pitted just 
in front of it ; the exoccipitals also contribute slightly to its 
formation. Slightly in front of and ventral to the foramen 
magnum is a small foramen through which the hypoglossal 
nerve leaves the cranial cavity. 

The supra-occipital is separated from the parietal by a 
suture line along which run a pair of prominent ridges, the 
lambdoidal crests (fig. 60, B, 30). There are often a pair of 
prominent vacuities in the supra-occipital dorsal to the foramen 
magnum. The epi-otics and opisthotics become completely 
fused with the bones of the occipital segment at a very early 
stage. 

(c) The ventral surface of the cranium is wide behind, 
where it is formed by a broad transverse membrane bone, the 
basiternporal (fig. 60, A, 23), the sides of which are fused with 
the auditory capsules. Slightly in front of and an eighth of 
an inch external to the hypoglossal foramen the cranial wall is 
pierced by a pair of foramina through which the tenth or 
pneumogastric nerves leave (fig. 60, A, X). At the sides 
of the basiternporal are a pair of depressions, the tympanic 
recesses, in each of which are three holes. Straight lines 
joining these holes would form an isosceles triangle with its 
apex directed forwards. Of the two holes at the base of the 
triangle, the one nearer the middle line and leading into the 
cranial cavity, is for the exit of the ninth or glossopharyngeal 
nerve (fig. 60, A, IX), it lies just in front of the pneumogastric 
foramen. The more external leads into the tympanic cavity, 
while the more anterior at the apex of the triangle is the 
posterior opening of the carotid canal (fig. 60, A, 25), 
which traverses the base of the cranium, and during life 
lodges the carotid artery. 

The anterior end of the basiternporal is pierced near the 



316 THE VERTEBRATE SKELETON. 

middle line by a pair of holes, the anterior openings of the 
Eustachian canals ; while just in front of these and a little 
further removed from the middle line are the anterior openings 
of the carotid canals. Bristles passed in through the posterior 
openings of the carotid canals will emerge here (fig. 60, A, 27). 
In front of the basitemporal the base of the cranium is formed 
by the rostrum (fig. 60, A, 31), or thickened basal portion of 
the interorbital septum ; this bears two prominent surfaces 
with which the pterygoids articulate. In some kinds of 
duck these surfaces are borne by well-marked basi-pterygoid 
processes. 

(d) The side of the cranium. At the base of the posterior 
end is seen the deep tympanic cavity. The dorsal part of 
this is divided by a vertical partition into two halves ; of these 
the more anterior is the larger, and forms a deep funnel- 
shaped cavity, the posterior opening of the Eustachian 
canal (fig. 60, B, 26). A bristle passed into this opening 
emerges through the anterior opening of the Eustachian canal. 
The more posterior of the two is the fenestral recess (fig. 60, 
B, 28), and is in its turn divided by a slender horizontal bar 
into a dorsal hole, the fenestra ovalis, and a ventral hole, 
the fenestra rotunda. During life the fenestra ovalis lodges 
the proximal end of the columellar chain. Lying at the 
outer side and slightly dorsal to the tympanic cavity is a deep 
depression, the lateral tympanic recess, and immediately 
in front of this is the articular surface for the quadrate. 
The tympanic cavity is bounded below by the basitemporal, 
posteriorly by the exoccipital, and above by the squamosal, a 
membrane bone, which roofs over a good deal of the side of 
the cranium, and bears ventrally a prominent surface with 
which the quadrate articulates. Just in front of this is a 
large round hole, the trigeminal foramen (fig. 60, B, V), 
behind which the squamosal is drawn out into a short process. 

In front of the sqiiamosal there is a pi'ominent forwardly- 
projecting postfrontal process (fig. 60, 8), which ossifies 



SKELETON OF THE WILD DUCK. THE SKULL. 317 

from a different centre from that forming the squamosal, but 
in the adult is completely fused with it. 

The orbit forms a large more or less hemispherical cavity 
which lodges the eyeball. It is separated from its fellow of 
the opposite side by an imperfect partition, the interorbital 
septum. In the young skull it is seen to be bounded above by 
the frontal, with which the lachrymal (fig. 60, 7) is fused 
anteriorly, forming a large backwardly-projecting process : 
while behind it is bounded by the alisphenoid. The inter- 
orbital septum is formed by the ossification and coalescence of 
the mesethmoid in front, with the orbitosphenoid behind, 
and the rostrum below. The boundary of the orbit below 
is very imperfect, the zygoniatic arch being incomplete. 

The interorbital septum is pierced by the very prominent 
optic foramen (fig. 60, B, 2), just behind which are the two 
much smaller foramina for the exit of the oculomotor and 
pathetic (fig. 60, B, TV) nerves, the more anterior being that 
for the oculomotor. 

Above and slightly in front of the optic foramen is a 
median opening, the olfactory foramen. This leads into 
the cranial cavity behind, and in front is continued forwards 
as a groove between the interorbital septum and the frontal. 

(2) THE FACIAL PART OF THE SKULL. 

This includes the olfactory capsule and associated bones, 
and the upper jaw. 

The bones associated with the olfactory capsules are the 
nasals and vomer. The nasals (figs. 59 and 60, 5) lie on the 
dorsal surface immediately in front of the cranium, and are 
separated from one another by the nasal processes of the pre- 
rnaxillte. Each is completely fused in the adult with the 
corresponding maxilla and premaxilla, the three bones together 
forming the boundary of the anterior nares. The i-u/ner (fig. 
60, 19) is unpaired and forms a small median vertical plate 



318 THE VERTEBRATE SKELETON. 

lying ventral to the anterior continuation of the interorbital 
septum. 

The bones of the upper jaw consist on each side of two 
slender arcades which in front converge and are attached to 
the large beak, while behind they diverge but are united by 
the quadrate. 

The inner arcade is formed by the pterygoid and palatine. 
The pterygoid (fig. 60, 21) is a short flattened bone, which 
articulates behind with the quadrate, and on its inner side 
with a large flattened surface borne by the rostrum, in front 
it meets the palatine, or sometimes ends freely with a long 
antero-dorsally directed point. 

The palatine (fig. 60, 20) is a slender irregular bone flat- 
tened dorso-ventrally at its anterior end where it articulates 
with the beak, and laterally behind. It gives off at its 
posterior end a process, which is sometimes united with the 
vomer, sometimes projects forwards, and meets its fellow 
dorsal to the vomer. In the large space between it and the 
vomer is the opening of the posterior nares. 

The premaxillae (figs. 59 and 60, 2) are very large, and 
form nearly a third of the big shovel-shaped beak. They con- 
stitute the inner, and part of the front boundary of the an- 
terior nares, and send back a pair of nasal processes which 
partially separate the nasals from one another. 

The outer arcade forms the slender suborbital bar, 
and consists mainly of two rod-like bones, which in the adult 
are completely fused together. The posterior of these is the 
quadratojugal (figs. 59 and 60, 11) which articulates with the 
quadrate, the anterior is the small and slender juyal or malar 
(figs. 59 and 60, 10). The extreme anterior part of the bar is 
formed by the maxilla. The main part of the maxilla how- 
ever lies anterior to the suborbital bar, and extends forwards 
along the side of the premaxilla forming all the lateral part of 
the beak (figs. 59 and 60, 1); it also sends inwards a plate, 
the maxillo-palatine (fig. 60, A, 29), which completely fuses 



SKELETON OF THE WILD DUCK. THE SKULL. 319 

with its fellow in the middle line, and forms the posterior 
boundary of the anterior palatine foramen. The term 
desmognathous describes the condition of the skull in 
which the maxillo-palatines fuse with one another in the 
middle line in this way. 

The quadrate (fig. 60, 12), which unites the two arcades 
behind, is a stout irregular four-cornered bone forming the 
suspensorium. It articulates by its dorso-posterior corner 
with the squamosal, and by its antero-internal corner with the 
pterygoid. The middle of its ventral surface forms a hemi- 
spherical knob with which the mandible articulates, while its 
dorso-anterior border is drawn out into a long point which 
extends towards the interorbital septum. 

(3) THE MANDIBLE. 

The mandible or lower jaw consists of two rami which 
are flattened and fused together in the middle line in front, 
while behind they diverge from one another and articulate 
with the quadrates. 

Each ramus is composed of five bones fused together, one 
being a cartilage bone, and the other four membrane bones. 
The articular is the only cartilage bone of the mandible, 
it bears the double condyle (figs. 59 and 60, 13) or concave 
articular surface for the quadrate, and is drawn out behind 
into a large hooked posterior articular process. The ar- 
ticular is also drawn out into a prominent process on each 
side of the articular surface for the quadrate, and is marked 
by a deep pit opening posteriorly. The articular is continuous 
in front with Meckel's cartilage which forms the original 
cartilaginous bar of the lower jaw, and is ensheathed by the 
membrane bones. Of these the supra-angular forms the upper 
part of the mandible in front of the articular, its dorsal sur- 
face is drawn out into a small coronoid process, its outer 
surface also bearing a prominent process. The angular is 



320 THE VERTEBRATE SKELETON. 

a small bone which underlies the articular and supra-angular 
on the inner side of the jaw. The dentary (fig. 59, 15) forms 
the anterior half of each ramus, and is the largest bone of the 
mandible ; it is fused with its fellow at the symphysis in front, 
and extends back below the supra-angular. The splenial is a 
small bone lying along the middle half of the inner side of 
each ramus of the mandible. 

(4) THE HYOID. 

With the hyoid apparatus is included the columella. 
This forms a minute rod of bone, one end of which is ex- 
panded and fits into the fenestra ovalis, while the other end, 
terminated by a triradiate piece of cartilage, is attached 
to the tympanic membrane. The structure is as a whole 
homologous with the auditory ossicles of mammals and the 
hyomandibular of fish. 

The hyoid consists of a median unpaired portion, formed 
of two pieces of bone, the basi-hyal (fig. 59, C, 16) in front, 
and the uro-hyal (fig. 59, C, 17) behind, the two being placed 
end to end and terminated anteriorly by an unpaired carti- 
laginous plate, the OS entoglossum. At the posterior end 
there come off a pair of long posterior cornua, each of 
which consists of two pieces, a longer basibranchial (fig. 59, 
C, 18), and a shorter ceratobranchial. For the homology of 
these parts see p. 336. 

THE RIBS AND STEHNUM. 

The last two cervical vertebrae bear long movable ribs 
which articulate by distinct capitular and tubercular processes, 
but do not meet the sternum. The thoracic ribs are eight in 
number, and each is divisible into a vertebral and a sternal 
portion. The first five thoracic ribs are flattened curved bars 
of bone, which articulate by a prominent capitulum with 
the centrum of the corresponding vertebra, and by a tuber- 
CTllum. with the transverse process. Projecting backwards 
from each is a large hooked uncinate process. The last t hrcr 



SKELETON OF THE WILD DUCK. THE STERNUM. 321 

ribs which are without uncinate processes, become progressively 
more slender, and in the eighth the tubercular processes are lost. 
The sternal portions of the ribs are imperfectly ossified 
pieces, short and comparatively thick in the case of the anterior 
ribs, longer and more slender in the case of the posterior ribs. 

THE STERNUM 1 . 

The sternum or breast bone is exceedingly large in the 
Duck, as in allbirds, and projects back far beyond the thorax over 
much of the anterior part of the abdomen. It is an irregularly 
oblong plate of bone, abruptly truncated behind, somewhat 
concave dorsally, and drawn out ventrally into a prominent keel, 
the carina, which projects for some distance forwards beyond 
the body of the sternum, and tapers off gradually behind. 
The point where the carina joins the body of the sternum is at 
the anterior end drawn out into a small process, the rostrum 2 .% 
Just dorso-lateral to this are a pair of deep grooves, the 
coracoid grooves, with which the coracoids articulate. 

The sides of the sternum are drawn out in front into a 
pair of short blunt costal processes ; and just behind these 
are a series of seven surfaces with which the ends of the 
sternal ribs articulate. Immediately behind these surfaces 
the sides are produced into a pair of long backwardly-pro- 
jecting xiphoid processes which nearly meet processes from 
the posterior end of the sternum. 

2. THE APPEXDICULAR SKELETON. 

This consists of the skeleton of the anterior and posterior 
limbs and of their respective girdles. 

A. THE PECTORAL GIRDLE'. 

The pectoral girdle in almost all birds is strongly constructed 
and firmly united to the sternum. It consists of three bones, 
a dorsal element, the scapula, a posterior ventral element, the 
coracoid. and an anterior ventral element, the clavicle. 

1 Cp. fig. 63. 

2 Often called the manubrium, but not homologous with the manu- 
brium of the mammalian sternum. 

R. 21 



322 THE VERTEBRATE SKELETON. 

The scapula forms a long curved flattened bone expanded 
at its anterior end, where it meets the coracoid, and lying 
across the ribs at its tapering posterior end. It helps to form 
the imperfect glenoid cavity, with which the humerus arti- 
culates. The coracoid, a shorter but stouter bone than the 
scapula, has its upper end or head thickened and bears on its 
posterior border an irregular surface, with part of which the 
scapula articulates, while the rest forms part of the glenoid 
cavity. The inner border of the coracoid adjoining the arti- 
cular facet for the scapula is produced into a strong process 
which helps to complete the foramen triosseum, a space 
lying between the adjoining ends of the scapula and coracoid, 
through which the tendon of the second pectoral muscle passes. 
The lower part of the coracoid, which is much flattened and 
^xpanded, and abruptly truncated posteriorly, articulates 
with the coracoid groove of the sternum. The clavicle is a 
thickened curved membrane bone, which is fused with its 
fellow in the middle line below, the two forming the furcula 
or merrythought. Its dorsal end is drawn out into a process 
which articulates with the coracoid. 

THE ANTERIOR LIMB OR WING. 

This consists of three parts, a proximal part, the upper arm 
or brachium, a middle part, the fore-arm or antibrachium, 
and a distal part, the manus. When extended for flight the 
parts lie almost in the same straight line, but when at rest they 
are folded on one another in the form of a Z, the brachium and 
manus pointing backwards, and the antibrachium forwards. 
When extended for flight the surfaces and borders of the wing 
correspond in position with those of the primitive vertebrate 
limb 1 , the pre-axial border being directed forwards and the post- 
axial backwards, while the dorsal and ventral surfaces look 
respectively upwards and downwards. But when the winy is 
at rest, the humerus as it extends backwards becomes slightly 
rotated, so that its dorsal surface looks more inwards than 
1 See p. 28. 



SKELETON OF THE WILD DUCK. THE WING. 323 

upwards, while the dorsal surface of the antibrachium looks 
partially outwards and upwards, and that of the manus mainly 
outwards. 

The brachium or upper arm contains only a single bone, 
the humerus (fig. 57, 1). This is a large nearly straight bone 
expanded at both ends. The proximal end is specially ex- 
panded, forming two tuberosities, and a large convex head 
articulating with the glenoid cavity. The pre-axial tube- 
rosity is the smaller of the two, but is continued by a 
prominent deltoid ridge, which extends for a very short 
distance down the shaft. The postaxial tuberosity is the 
larger, and below it there is a very deep pit, the pneumatic 
foramen, which leads into an air cavity in the shaft of the 
bone. The shaft is long and straight, and at the distal end 
of the bone is the trochlea with two convex surfaces, one 
pre-axial with which the radius articulates, the other post- 
axial for the ulna. 

The fore-arm or antibrachium consists of two bones, 
the radius and ulna. These are of nearly equal length, and 
are separated from one another by a considerable space except 
at their terminations. 

The radius (fig. 57, 2), the pre-axial and smaller bone, is 
straight and fairly stout ; its proximal end articulates with 
the humerus by a slightly cupped surface, while its distal end, 
which articulates with the carpus, is convex and somewhat 
expanded. 

The ulna (fig. 57, 3) is longer, stouter, and slightly curved. 
Its proximal end is expanded, forming two surfaces which 
articulate with the trochlea of the humerus ; behind them it 
is drawn out into a short blunt olecranon process. Its 
distal end is less expanded, and articulates with the carpus 
and also with the radius. 

The Manus. This includes the carpus or wrist, and the 
hand. 

The Carpus. While in the embryo the carpus consists 

212 



324 THE VERTEBRATE SKELETON. 

of five distinct elements arranged in a proximal row of two 
and a distal row of three, in the adult only the proximal 
bones can be clearly distinguished, the distal ones having 
become completely ankylosed with the metacarpals to form 
the carpometacarpus. 

The two distinct carpal bones are the radial carpal and 
the ulnar carpal. The radial carpal (fig. 57, 4) is a small 
somewhat cubical bone, wedged in between the manus and 
the radius and ulna. The ulnar carpal (fig. 57, 5) is a 
somewhat larger, more irregular bone, lying adjacent to the 
end of the ulna. It is deeply notched to receive the carpo- 
metacarpus. 

The hand. In the adult bird the hand is in a much 
modified condition ; only the first three digits are represented, 
and the metacarpals are all fused with one another and with 
the distal carpalia to form the carpo-metacarpus. 

The most prominent part of the carpo-metacarpus is formed 
by the second metaearpal (fig. 57, 7), a stout, straight bone 
expanded at both ends. The third metaearpal (fig. 57, 8) 
is a more slender curved bone fused at both ends with the 
second metaearpal. The first metaearpal forms simply a 
small projection on the radial side of the proximal end of the 
second metaearpal. 

The phalanges. The first digit or pollex includes two 
phalanges, the distal one being very small and bearing a claw. 

The second digit includes three phalanges, the proximal 
one being somewhat flattened. The third digit has a single 
small phalanx. 

THE PELVIC GIRDLE. 

The bones constituting the pelvic girdle are not only as in 
other higher vertebrates ankylosed together forming the in- 
nominate bones, but are also ankylosed with a series of some 
seventeen sacral and pseudosacral vertebrae. The acetabulum 
(fig. 61, 5) with which the head of the femur articulates is 
incompletely ossified. 



SKELETON OF THE WILD DUCK. PELVIC GIRDLE. 325 

The ilium (figs. 58 and 61, 1) is the largest bone of the 
pelvis. It forms a long flattened plate extending for a con- 
siderable distance both in front of and behind the acetabulum, 
and is fused along its whole length with the transverse pro- 
and neural spines of the sacral and pseudosacral verte- 
brae. It forms more than half the acetabulum, above and 




FIG. 61. LATERAL VIEW or THE PELVIS AND SACRCM OF A DUCK (Anas 
boschag) x f . 

1. ilium. 5. acetabulntu. 

2. ischium. 6. ilio-sciatic foramen. 

3. pubis. 7. fused vertebrae. 

4. pectineal process. 8. antitrochanter. 

behind which it is produced to form a process, the antitro- 
chanter (fig 61, 8), with which the great trochanter of the 
femur articulates. 

The ischium (figs. 58 and 61, 2) is a flattened bone which 
forms about one-third of the acetabulum, and lies ventral to the 
posterior part of the ilium. Its anterior portion is separated 
from the ilium by the large oval ilio-sciatic foramen (fig. 
61, 6), while behind this the two bones are completely fused. 

The pubis (figs. 58 and 61, 3) is a very long slender bar 
of bone which forms only a very small part of the acetabulum 
and runs back parallel to the ventral surface of the ischium 
with which it is loosely connected at its posterior end. For 
the greater part of their length the two bones are separated by 



326 THE VERTEBRATE SKELETON. 

the long narrow obturator foramen. Behind the ischium 
the pubis is produced into a long curved downwardly-project 
ing process, and in front of the acetabulum it bears a short 
blunt pectineal or pre-pubie process (fig. 61, 4) probably 
homologous with the pre-pubis of Orthopod Dinosaurs. The 
remainder of the pubis is homologous with the post-pubis of 
Orthopod Dinosaurs. 

THE POSTERIOR LIMB. 

The leg of the bird is somewhat differently constructed from 
that of other vertebrates owing to the fact that there is no 
free tarsus, the proximal tarsals having fused with the tibia, 
and the distal with the metatarsals. 

The thigh consists of a single bone, the femur. The femur 
is a comparatively short bone with a straight shaft and ex- 
panded ends. The proximal end bears on its inner side a 
rounded head, which articulates with the acetabulum. On its 
outer side is an irregular outgrowth, the great trochanter, 
while between the two is the surface which meets the antitro- 
chanter of the ilium. The posterior end also is expanded 
and marked by a wide groove which lodges the patella. On 
each side of the groove is a strong condylar ridge for articu- 
lation with the tibia. The external condyle is deeply grooved 
behind for articulation with the fibula. 

The crus or shin consists of two separate bones, (1) the 
tibio-tarsus, formed by the fusion of the tibia with the proxi- 
mal row of tarsals, and (2) the fibula. 

The tibio-tarsus is a thick straight bone nearly twice as 
long as the femur. Both ends of the bone are considerably 
expanded. The proximal end bears two slight depressions 
which articulate with the condyles of the femur, and a third 
depression which partly lodges the patella. The proximal end 
of the anterior or extensor surface is drawn out into a very 
prominent cnemial crest which bends over towards the post- 
axial side of the bone ; a slight ridge is continued from it all 



SKELETON OF THE WILD DUCK. THE PES. 327 

the way down the shaft. The proximal part of the shaft of 
the tibio-tarsus bears a roughened ridge with which the fibula 
is closely connected. The distal end is expanded and rotated 
outwardly and forms a prominent pulley-like surface which 
articulates with the tarso-metatarsus. 

The fibula is reduced to the proximal portion only, which 
is expanded and articulates with a depression behind the 
external condyle of the femur. The fibula further extends 
about a third of the way down the shaft of the tibio-tarsus. 
The patella or knee-cap is a sesamoid bone due to an ossi- 
fication in the tendon of the extensor muscles of the leg. 

The ankle joint lies between the proximal and distal 
tarsals which as previously mentioned fuse respectively with 
the tibia and metatarsus. 

The Pes. The pes includes four digits, and consists of the 
tarso-metatarsus and the phalanges. The proximal tarsals 
which are fused with the tibia also really belong to the pes. 

The tarso-metatarsus is a strong straight bone nearly as 
long as the femur, and is formed by the fusion of the distal 
tarsals with the second, third and fourth metatarsals. The 
proximal end of the bone is expanded and bears two facets for 
articulation with the tibio-tarsus, and near them on the pos- 
terior surface is a large roughened projection. The lines of 
junction between the several metatarsals are marked along 
the shaft by slight ridges. At the distal end of the bone the 
three metatarsals diverge from one another aud each bears a 
prominent convex pulley-like surface. The first metatarsal 
is reduced to the distal end, which tapers to a point proximally, 
and is attached by ligaments near the distal end of the tarso- 
metatarsus. 

The digits. Four digits are present, each consisting of a 
metatarsal (already described) and a certain number of pha- 
langes, the terminal one being in each case clawed. The first 
digit or hallux has two phalanges, the second three, the third 
four, and the fourth five. 



CHAPTER XIX. % 

GENERAL ACCOUNT OF THE SKELETON IN 
BIRDS. 

EXOSKELETON. 

The epidermal exoskeleton of birds is very greatly de- 
veloped, feathers constituting its most important part. 

Three kinds of feathers are found, viz. (a) pennae including 
quills and coverts, (6) down feathers or plumulae, and (c) filo- 
plumes which are rudimentary feathers. The structure of 
the different kinds of feathers is described on pp. 303 306. 

Sometimes a fourth class of feathers, the semiplumae, is 
recognised. They have the stems of pennae, and the downy 
barbs and barbules of plumulae. 

In most birds the pennae are riot uniformly distributed 
over the whole surface of the body, but are confined to certain 
tracts, the pterylae ; while the intervening spaces or apteria 
are either bare or covered only with down feathers. In some 
birds, however, such as the Ratitae and the Penguins, pennae 
are evenly distributed over the whole body. 

In many birds the calamus or quill bears two vexilla or 
vanes, the second of which, called the altershaft or hypo- 
rachis, is generally much the smaller, and is attached to the 
under surface of the main vexillum. In the Moas, Emeu and 
Cassowary the two vexilla in the adult bird are nearly equal 
in size ; though in the nestling Emeu one is much longer than 
the other. The aftershaft is very small in most Passeres and 
gallinaceous birds, but is comparatively large in Parrots, Gulls, 



THE SKELETON IX BIRDS. THE EXOSKELETON. 329 

Herons and most birds of prey. It is absent or extremely 
small in the Ostrich, Apteryx, Rhea, Pigeons, Owls, Anseres, 
and others. 

The quill feathers include two groups, the remiges or 
wing quills, and the rectrices or tail quills. In most birds 
the primary remiges, or those which are attached to the bones 
of the manus, are ten or eleven in number, and are set in 
grooves in the bones, being firmly attached to them. In the 
Ostrich however the primaries are little specialised in character 
and are as many as sixteen in number. They are also less 
definitely attached to the bones ; as their ends do not lie in 
grooves in the bones, but project beyond them. 

The secondary quills or those attached to the ulna vary 
much in number according to the length of the bone. The 
large dark quills in the wings of Cassowaries are the second- 
aries. 

The wing of Penguins is very little differentiated. It 
is covered at the margin by overlapping scales which gradually 
merge into scale-like feathers at the proximal end. The wing 
of the Penguin has nothing comparable to the remiges of other 
birds. 

In some birds, such as Herons (Ardea), there occur in 
places plumulae of a peculiar kind, which grow persistently 
and whose summits break off into fine powder as fast as they 
are formed. These feathers are known as powder -down 
feathers. They occur also in some Parrots and are then 
scattered indiscriminately all over the body. 

Other exoskeletal structures besides feathers are commonly 
well developed. Thus the extremities of the jaws are sheathed 
in horny beaks whose form varies enormously according to 
the special mode of life. 

In ducks and geese the beak with the exception of the 
anterior end is soft, and its edges are raised into lamellae, 
while in the Mergansers these lamellae become pointed pro- 
cesses supported by bony outgrowths. These lamellae act as 



330 THE VERTEBRATE SKELETON. 

strainers. In Parrots and Hawks, on the other hand, nearly 
the whole of the beak is hard. 

The toes and tarso-meta tarsus are usually featherless and 
are covered either with granular structures or with well- 
formed scales. The toes are nearly always provided with 
claws, and these vary in correlation with the character of the 
beak. Claws 1 also sometimes occur on the manus. Thus 
Archaeopteryx and some Ostriches and Rheas nave claws on 
all three digits. Most Ostriches and Rheas, and many Anseres 
and birds of prey, have them on the first two digits, while the 
Secretary bird (Gypogeranus] and many fowls, ducks, and birds 
of prey, especially kestrels, have a claw only on the pollex. 
In the Cassowary, Emeu, Apteryx and some Ostriches and 
Rheas only the second digit is clawed. 

Claws should not be confounded with spurs, which are 
conical horny structures developed on bony outgrowths of 
the radial side of the carpus, metacarpus, or metatarsus. 
They occur in a number of birds, but are most commonly 
developed in gallinaceous birds, by which they are used for 
fighting. A single spur occurs on the metacarpus in Mega- 
podius, in Palamedea, in Parra jacana and in Hoplopterus 
spinosus, the Spur-winged plover. The Derbian Screamer, 
Chauna derbiana, has two metacarpal spurs, borne on the 
first and second metacarpals. The Spur-winged goose, Plec- 
tropterus gambensis, has a carpal spur borne on the radial 
carpal. Metatarsal spurs are quite common. 

The male Solitaire (Pezophaps] has large bony excrescences 
on the wrist which may, like spurs, have been sheathed in 
horn and used for fighting. 

Teeth do not occur in any living birds, but conical teeth 
imbedded in separate sockets are present in Archaeopteryx 
and Ichthyornis, while in Hesperorrtis similar teeth occur im- 
planted in continuous grooves in the mandibles and maxillae, 
the premaxillae being toothless. 

1 W. K. Parker, Phil. Trans, vol. 179, p. 385, 1888 ; and Ibis, 1888, p. 124. 



THE SKELETON IN BIRDS. THE ENDOSKELETOX. 331 



Except that teeth are partly dermal in origin, a dermal 
exoskeleton is quite unrepresented in birds. 

EXDOSKELETOX. 

Perhaps the most striking feature of the endoskeleton of 
birds is its pneumaticity. In the embryo all the bones con- 
tain marrow, but as growth proceeds this becomes replaced by 
air to a variable extent in. different forms. In all birds some 
part of the skeleton is pneumatic. Many small birds and 
Apf>-ryx and Penguins among larger ones have air only in the 
skull : in Pigeons air is present in all the bones except the 
caudal vertebrae, the leg bones, and those of the antibrachium 
and manus : in Hornbills every bone contains air. 




FIG. 62. THIRD CERVICAL VERTEBRA OF AX OSTRICH (Stritthio camelus). 
x 1. A anterior, B posterior, C dorsal view (A and B after MIVABT). 

6. anterior articular surface of 

centrum, 
vertebrarterial canal. 



1. neural spine. 

2. neural canal. 

3. prezygapophysis. 

4. postzygapophysis. 

5. posterior articular surface of 

centrum. 



7. 

8. hypapophysis. 



332 THE VERTEBRATE SKELETON. 

VERTEBRAL COLUMN. 

The vertebral column of birds is readily divisible into a 
very mobile cervical region, and an extremely rigid post- 
cervical region. In most birds the vertebral centra are with- 
out terminal epiphyses, but these structures are found in 
Parrots. The cervical vertebrae are generally large and vary 
in number from eight or nine to twenty -three in Swans. 
Except in some extinct forms, such as Ichthyornis and Apa- 
tornis, in which they are biconcave, the centra are charac- 
terised by having saddle-shaped articulating surfaces, which 
in front are concave from side to side and slightly convex 
from above downwards, while posteriorly they are convex 
from side to side and concave from above downwards. The 
atlas is small and ring-like, and its centrum is fused with the 
axis forming the odontoid process. Cervical ribs are often 
well developed, and in some of the Ratitae they remain for a 
long time distinct from the vertebrae. 

The thoracic vertebrae are distinguished from the cervical 
by the fact that their true ribs are united to the sternum 
by means of sternal ribs. This distinction, however, though 
convenient, is somewhat arbitrary, as it has been shown that 
in the fowl and gannet, two pairs of ribs which in the adult 
are free from the sternum, are connected with it in the em- 
bryo. When, as in the Swans, the thoracic vertebrae are 
not all fused together, they generally have saddle-shaped 
articulating surfaces, but sometimes, as in the Penguins, Auks 
and Plovers, the centra are convex in front and concave be- 
hind. The trunk vertebrae generally have well-marked neural 
spines, while in the Divers the anterior ones have peculiar 
bifurcating hypapophyses. 

The trunk vertebrae are not readily divisible into thoracic 
and lumbar. There are two true sacral vertebrae, but as 
development proceeds a number of other vertebrae become 
fused with the true sacrals, the whole forming a large com- 
pound sacrum. These pseudosacral vertebrae generally include 



THE SKELETON IN BIRDS. THE SKULL. 333 

the lumbar, and some of the thoracic and caudal vertebrae. 
Sixteen to twenty vertebrae or even more may be included 
in the compound sacrum, and sometimes the whole of the 
trunk vertebrae are fused together. In Archaeopteryx however 
but five vertebrae take part in the formation of the sacrum. 

In Archaeopteryx there are twenty long caudal vertebrae, 
of which the last sixteen carry a pair of feathers apiece, but 
in all other birds the tail is short and in the great majority 
of cases the posterior vertebrae are fused together, forming the 
pygostyle. In the Ratitae and Tinamidae a pygostyle is rarely 
or imperfectly developed. In Hesperornis there are twelve 
caudal vertebrae, six or seven of which are united by their 
centra only, forming an imperfect pygostyle. 

The free caudal vertebrae are generally amphicoelous. 

THE SKULL. 

The skull of all birds from Archaeopteryx onwards is 
essentially similar, differing from the skull of reptiles mainly 
in the extent to which the cranium is arched, and its greater 
size in proportion to the jaws. 

Most of the bones of the cranium are pneumatic, and all 
show a marked tendency to fuse together, and have their 
outlines obliterated by the disappearance of the sutures. The 
several bones remain longest distinguishable in the Ratitae 
and to a less extent in the Penguins. The orbits are very 
large and lie almost entirely in front of the cranium ; they 
are separated by an interorbital septum which is sometimes, as 
in Chauna and Scythrops, very complete, sometimes, as in 
Hornbills and the Common Heron, very slightly developed. 
As a general rule the sclerotic is cartilaginous. 

The anterior nares are almost always situated far back 
at the base of the beak near the orbits, but in Apteryx they 
are placed right at its extremity. In Phororhacos they are 
placed very high up on the enormous beak and are not separ- 
ated by any bony partition. 



334 THE VERTEBRATE SKELETON. 

The skull of Parrots has some peculiarities. In some 
Parrots the lachrymal sends back a process which meets the 
postorbital process of the frontal and completes the orbit. 
In most birds the upper beak is immovably fixed, but in 
some it is attached to the cranium, only by the nasals and 
by flexible processes of the premaxillae, so that by this 
means a kind of elastic joint is established and the beak is able 
to be moved on the cranium. In the Parrots and Opisthocomus 
there is a regular highly movable joint. 

In Cassowaries the fronto-nasal region of the skull is pro- 
duced into an enormous bony crest, and in Hornbills a 
somewhat similar structure occurs. Although true teeth do 
not occur in any known bird except Archaeopteryx, Hesper- 
ornis, and Ichthyornis, another extinct bird, Odontopteryx, has 
the margins of both jaws provided with forwardly -directed 
tooth-like serrations, formed of part of the actual jawbone: a 
living hawk, Harpagus, too, has a deeply notched bill, to 
which correspond serrations in the premaxillae. 

A basipterygoid process of the basisphenoid abuts against 
the pterygoid in Ratitae and in Tinamous, plovers, fowls, 
pigeons, ducks and geese among Carinatae, recalling the 
arrangement met with in many reptiles. The squamosal is 
sometimes, as in the fowl, united with the postorbital process 
of the frontal. In the Carinatae the quadrate articulates 
with the cranium by a double convex surface, in the Ratitae 
by a single one. The premaxillae are always comparatively 
large bones, the maxillae on the contrary are small, but 
give rise to important inwardly-projecting maxillo-palatine 
processes. 

The relations of the palatines, pterygoids, maxillae, and 
vomers vary considerably, and on them Huxley has based a 
classification of birds'. In the Ratitae and the Tinamous 
(Tinamidae), among Carinatae the vomers unite and form a 
large broad bone, separating the palatines and the pterygoids 
1 See T. H. Huxley, "On the Classification of Birds," P. Z. S. 1867. 



THE SKELETON IX BIRDS. THE SKULL. 335 

from the rostrum. Huxley uses the term Dromaeognathous 
to describe this condition. In all other Carinatae the vomers 
are narrow behind, and the palatines and pterygoids converge 
posteriorly and articulate largely with the rostrum. Three 
modifications of this condition are distinguished by Huxley, and 
termed Schizognathous, ^Egithognathous, and Desmo- 
gnathous. 

In the Schizognathae the vomers coalesce and form a 
narrow elongated bone, pointed in front, separating the 
maxillo-palatine processes of the premaxillae. Waders, fowls, 
penguins, gulls, some falcons and eagles, American vultures, 
some herons and many owls have the Schizognathous arrange- 
ment. In pigeons and sandgrouse there is no vomer, but the 
other bones have the Schizognathous arrangement. 

In the -(Egithognathae the arrangement is the same as in 
the Schizognathae, except that the vomers are truncated in 
front Passeres, swifts, woodpeckers, humming birds, rollers, 
hoopoes have this arrangement. 

In the Desmognathae (fig. 60, A) the maxillo-palatine 
processes approach one another in the middle line, and either 
unite with the vomers, or unite with one another, hiding the 
vomers. Thus a more or less complete bony roof is formed 
across the palate. The vomers in Desmognathae are small or 
sometimes absent. Ducks, storks, most herons, most birds of 
prey and owls, pelicans, cormorants, parrots, and flamingoes 
are Desmognathous. 

The mandible, as in other Sauropsids, consists of a cartilage 
bone, the articular, and a series of membrane bones, the 
dentary, splenial, coronoid, angular, and supra-angular, de- 
veloped round the unossified Meckel's cartilage. The dentaries 
of the two rami are nearly always fused together, but in 
Ichthyornis and Archaeopteryx the two rami are but loosely 
united. There is often a fontanelle between the dentary and 
the posterior bones, while the angle is sometimes, as in the 
fowl, drawn out into a long curved process. 



336 THE VERTEBRATE SKELETON. 

The hyoid apparatus (fig. 59, C) consists of a median 
portion, and a pair of cornua. The median portion is com- 
posed of three pieces placed end to end, and called respectively 
the os entoglossum, the basi-hyal, and the uro-hyal. The os 
entoglossum is shown by development to be formed by the 
union of paired structures and is probably homologous with the 
hyoid arch of fishes. The basihyal and the long cornua, each 
of which is composed of two or three pieces placed end to end, 
are homologous with the first branchial arch of fishes, while 
the urohyal is probably homologous with the second branchial 
arch of fishes. In Woodpeckers the cornua are enormously 
long, and curve over the skull, extending as far forwards as 
the anterior nares. 

RIBS AND STERNUM. 

Well-developed ribs are attached to the posterior cervical 
vertebrae as well as to the thoracic vertebrae. The ribs 
generally have uncinate processes and separate capitula and 
tubercula, but uncinate processes are absent in Chauna Pala- 
medea and apparently in Archaeopteryx. 

The sternum (tig. 63) is greatly developed in all birds. In 
the embryo 1 it is seen to be derived from the union of right 
and left plates of cartilage, formed by the fusion of the ventral 
ends of the ribs. In the Ratitae and a few Carinatae, such 
as Stringops, it is flat, but in the great majority of birds 
it is keeled, though the development of the keel varies greatly. 
It is large in the flightless Penguins, which use their wings 
for swimming. Traces of an interclavicle may occur in the 
embryo. 

PECTORAL GIRDLE. 

The pectoral girdle is also strongly developed in all 
Carinatae, but is much reduced in Ratitae. In some Moas 
the sternum has no facet for the articulation of the coracoid, 
and the pectoral girdle appears to have been entirely absent ; 

1 B. Lindsay, P. Z. S. 1885, p. 684. 



THE SKELETON IX BIRDS. THE PECTORAL GIRDLE. 337 

A C 




FIG. 63. SHOCLDEE-GIBDLE AND STERNUM OF 

A. BLACK YULTUHE (Vultur cinereus)x\. 

B. PEACOCK (Paro crittatus) x f . 

C. PELICAN (Pelicanus conspicillatus) x $. (All Camb. Mus.) 

1. carina of the sternum. 6. surfaces for articulation with 

2. coracoid. the sternal ribs. 

3. scapula. 7. xiphoid processes. 

4. clavicle. 8. fontanelle. 

5. costal proce 

R. 22 



338 THE VERTEBRATE SKELETON. 

it is extremely small also in Apteryx. Clavicles are generally 
well developed in the Carinatae, and small ones are found 
also in Hesperornis, and in Emeus and Cassowaries. In the 
other living Ratitae and in Stringops they are absent. In 
some Parrots, Owls and Toucans they do not meet one another 
ventrally. Clavicles are especially stout in some of the birds 
of prey. They do not generally touch the sternum, but some- 
times, as in the Pelican (fig. 63, C), Adjutant and Frigate bird, 
they are fused with it. 

In all Ratitae the scapula and coracoid lie almost in the 
same straight line with one another, in the Carinatae they are 
nearly at right angles to one another. 

ANTERIOR LIMB. 

In the wing of nearly all birds the ulna is thicker than the 
radius, but in Archaeopteryx the two bones are equal in size. 
In the wing of Archaeopteryx there are three long digits with 
distinct metacarpals. In all other birds the digits are modi- 
fied, the metacarpals being commonly fused and the phalanges 
reduced in number. In Pcdamedea and some other birds the 
metacarpus bears a bony outgrowth, which when sheathed in 
horn forms a spur. 

In most of the Ratitae and in the extinct Dodo (Didus) 
and Solitaire (Pezophaps) the wing is very small, but the 
usual parts are recognisable. In Hesperornis apparently only 
the humerus is present ; in some Moas, in which the wing is 
imperfectly known, the presence of the humerus is indicated 
by traces of a glenoid cavity. In most Moas the wing is 
apparently completely absent. As compared with those in other 
Ratitae, the wings of the Ostrich and Rhea are well developed. 
In the Ostrich (fig. 64, B) and Rhea, as in nearly all Carinatae, 
the manus has three digits, but in Apteryx there is only a single 
digit, the second. The Penguins (fig. 64, A) too among Cari- 
natae have only two digits, but in their case it is the pollex 
which is missing. In the Ostrich the third digit has two 
phalanges, in all other living birds it has only one phalanx. 



THE SKELETON IX BIRDS. THE PELVIC GIRDLE. 339 



PELVIC GIRDLE. 

Birds have a very large pelvis and its characters are 
constant throughout almost the whole group. The ilium 

A 





FIG. 64. BONES OF THE RIGHT WING OF 

A. A PENGUIN x i. (Camb. Mus.) 

B. OSTRICH (Struthio camelu.i) x i. (Partly after PARKER.) 

C. GANNET (Sula aZfca) x . (Camb. Mus.) 

In C the distal phalanges of the pollex and second digit have been 
omitted. 



1. humerus. 

'2. radius. 

3. ulna. 

4. second metacarpal. 
n. third metacarpal. 



6. pollex. 

7. second digit. 

8. cuneiform. 

9. sesamoid bone. 



is very large, and is united along its whole length with 
the sacral and pseudosacral vertebrae. The ischium is broad 
and extends back parallel to the ilium with which in most 

22 2 



340 



THE VERTEBRATE SKELETON. 




FIG. 65. PELVIC GIRDLE AND SACBUM OF 

A. CASSOWABY (Casuarius galeatus) x . 

B. OWEN'S APTERYX (A. oweni)x\. 

C. BROAD BILLED BHEA (JR. macrorhyncha)x$. 

D. OSTBICH (Struthio camelus) x T V- (All Camb. Mus.) 

4. acetabulum. 



1. ilium. 

2. ischium. 

3. pubis. 



5. pectineal process. 



THE SKELETON IN BIRDS. THE PELVIC GIRDLE. 341 

birds it fuses posteriorly, further forward the ilio-sciatic 
foramen separates the two bones. In Tinamus, Hesperornis, 
Apteryx (fig. 65, B, 2), and Struthio, the ischia are separate 
from the ilia along their whole length except at the acetabu- 
lum ; in Phororhacos, on the other hand, the two bones are 
fused along almost their whole length. The bone usually 
called the pubis in birds corresponds to the post-pubis of 
Dinosaurs and forms a long slender rod (fig. 65, 3) lying 
parallel to the ischium. In many birds the ischia and pubes 
are united at their distal ends. This is the case in the Ostrich 
(fig. 65, D), in which the ilia and ischia are widely separated. 
In many birds the pubis is drawn out in front into the pectineal 
process, this is specially large in Apteryx (fig. 65, B, 5), and in 
the embryos of many birds. It is probably homologous with the 
pre-pubis of Dinosaurs but in some birds is formed in part by 
the ilium. The acetabulum in birds is always perforate. 

In Khea (fig. 65, C, 2) and probably in Archaeapteryx a 
symphysis ischii occurs, and in the ostrich alone among birds 
there is a symphysis pubis. In Archaeapteryx all three bones 
of the pelvis are distinct, but they are imperfectly known. In 
Ichthyornis they are also distinct, in all other known birds 
they are fused together to a greater or less extent. 



The tibia is always well developed and has a very strong 
cnemial crest. The proximal tarsals are fused with its 
distal end, the whole forming a compound bone, the tibio- 
tarsus. There is frequently an oblique bar of bone crossing 
the anterior face of the tibio-tarsus at the distal end, just 
above the articular surface of the tarso-ruetatarsus, this is 
absent in Ostriches and ^Epyornis. The fibula though in the 
embryo and in Archaeopteryx equal in length to the tibia, is in 
the adult of other birds always imperfect, its proximal end 
is often fused with the tibia, and its distal end is commonly 
atrophied. In the Penguins however the distal end is com- 
plete. The distal tarsals fuse with the second, third and fourth 



342 THE VERTEBRATE SKELETON. 

metatarsals, forming a compound bone, the tarso-metatarsus. 
The first metatarsal is nearly always free but occasionally 
as in Phaethon it is fused with the others. No adult bird 
has more than four digits in the pes. In the Penguins the 
metatarsals are separate, and in many birds larger or smaller 
gaps exist between the fused metatarsals. In most birds 
the third metatarsal is curved so as not to lie in the same 
plane as the others, but in the Penguins they all three lie in 
the same plane. The metatarsals are clearly separated in 
Archaeopteryx. In Gallinaceous birds the tarso-metatarsus 
bears a bony outgrowth which is sheathed in horn and forms 
a spur. 

In most birds the first four toes are present while the fifth 
is always absent. The first toe commonly has two phalanges, 
the second three, the third four, and the fourth five. In 
Swifts the third and fourth toes have only three phalanges. 
Many birds, such as all Ratitae except Apteryx, have only three 
toes, the hallux being absent ; in the Ostrich the second toe is 
also gone with the exception of a small metatarsal, so that the 
foot retains only the third and fourth digits, the third being 
much the larger of the two and bearing a claw, while the 
fourth is clawless. 

In the Swifts, Cormorants, and Penguins, all four toes are 
directed forwards. In most birds the hallux is directed back- 
wards, and the other toes forwards. In the Owls the fourth 
toe can be directed backwards as well as the hallux, while 
in Parrots, Cuckoos, Woodpeckers, and Toucans the fourth toe 
is permanently reversed. In Trogons the second toe is reversed 
in addition to the hallux, but not the fourth. 



CHAPTER XX. 

CLASS MAMMALIA. 

THE skeleton of the members of this class, the highest of 
the vertebrata, has the following characteristics : 

Some part of the integument at some period of life is 
always provided with hairs; these are epidermal structures 
arising from short papillae of the Malpighian layer of the 
epidermis, which at once grow inwards and become imbedded 
in pits of the dermis. Sometimes scales or spines occur, and 
epidermal exoskeletal structures inHhe form of hoofs, nails, 
claws and horns are also characteristic. As regards the endo- 
skeleton, the vertebral centra have terminal epiphyses except 
in the Ornithodelphia and some Sirenia. In the skull the 
cranial region is greatly developed as compared with that in 
lower vertebrates, and whereas in many reptiles the true 
cranium is largely concealed by a false roof, in mammals the 
only relic of this secondary roof is found in the zygomatic 
arch, and postorbital bar. In the adult all the bones except 
the mandible, hyoid, and auditory ossicles are firmly united 
together. The basisphenoid is well ossified, and there is no 
parasphenoid. The pro-otic ossifies, and unites with the epi-otic 
and opisthotic before they coalesce with any other bones. 

The skull articulates with the vertebral column by means 
of two convex occipital condyles formed mainly by the ex- 
occipitalsr and the mandible articulates with the squamosal 
without the intervention of the quadrate. The latter is much 
reduced, and is converted into the tympanic ring, while the 
hyomandibular of fish is represented by the auditory ossicles 1 . 

1 This is Gadow's view ; according to Huxley the quadrate forms the 



344 THE VERTEBRATE SKELETON. 

The teeth are always attached to the maxillae, premaxillae 
and mandibles, never to any of the other bones. They are 
nearly always implanted in distinct sockets, and are hardly ever 
ankylosed to the bone. The teeth of mammals are generally 
markedly heterodont, four forms, incisors, canines, premolars, 
and molars, being commonly distinguishable. Some mammals 
are monophyodont, having only a single set of teeth, but the 
great majority are diphyodont, having two sets, a deciduous or 
milk dentition, and a permanent dentition. 

The incisors, the front teeth, are simple, one-rooted, adapted 
for cutting, and are nearly always borne by the premaxillae. 
Next come the canines, one on each side in each jaw. They are 
generally large .teeth adapted for tearing or holding, and get 
their name from the fact that they are largely developed in the 
dog. The remaining teeth form the grinding series, the more 
posterior of them being the molars, which are not preceded by 
milk teeth '. Between the molars and the canines are the pre- 
molars, which do as a rule have milk or deciduous predecessors, 
though very frequently the first of them is without a milk 
predecessor. 

In describing the dentition of any mammal, for the sake of 
brevity a formula is generally made use of. Thus, the typical 
mammalian dentition is expressed by the formula 

.31 4311 
^- 3 c I P^- m ^ = -, 

giving twenty-two teeth on each side, or forty-four altogether 2 . 
The incisors are represented by i, the canines by c, the pre- 
molars by p or pm, and the molars by m. The numbers above 
the lines represent the teeth in the upper jaw, those below 

malleus ; according to Baur it forms the zygomatic process of the squa- 
mosal, and according to Broom the interarticular mandibular cartilage. 

1 According to Leche, Morphol. Jahrb. xix. p. 502, the molar teeth 
belong morphologically to the first series, i.e. they are milk teeth without 
vertical successors. 

2 The researches of Bateson, P. Z. S. 1892, p. 102, have shown that 
cases of individual variation in the number of teeth are common. 



MAMMALIA. 345 

the lines the teeth in the lower jaw. The milk dentition is 
expressed by a similar formula with d (deciduous) prefixed to 
the letter expressing the nature of the tooth. 

The following terms are of frequent use as characterising 
certain forms of the grinding surfaces of teeth, and it will be 
well to define them at once. 

Bunodont is a term applied to teeth with broad crowns 
raised into rounded tubercles, e.g. the grinding teeth of Pigs 
and Hippopotami ; 

Bilophodont to teeth marked by a simple pair of trans- 
verse ridges, with or without a third ridge running along the 
outer border of the tooth at right angles to the other two, 
e.g. the grinding teeth of Lophiodon, Kangaroo, Manatee, 
Tapir, Dinotlwium ; 

Selenodont to teeth marked by crescentic ridges running 
from the anterior towards the posterior end of the tooth, e.g. 
the grinding teeth of the Ox and Sheep. 

Teeth whose crowns are low so that their whole structure 
is visible from the grinding surface are called brachydont, while 
those with higher crowns, in which the bases of the infoldings 
of enamel are invisible from the grinding surface are said to 
be hypsodont. Bunodont teeth are brachydont, the teeth of the 
Horse and Ox are hypsodont. 

Passing now to the appendicular skeleton the shoulder- 
girdle differs markedly from that of Sauropsids in the fact that 
the coracoid, except in the Ornithodelphia, is greatly reduced, 
generally forming only a small process on the scapula. In the 
pelvis the pubes meet in a ventral symphysis, except in some 
Insectivora and Chiroptera. In many mammals a fourth pelvic 
element, the acetabular bone, is distinguishable. The ankle 
joint is cmro-tarsal, or situated between the proximal tarsal 
bones and the tibia and fibula. Carpalia 4 and 5 are united 
forming the unciform; and the ulnar sesamoid bone or pisiform 
is generally well developed. In the proximal row of tarsal ele- 
ments there are only two bones, the calcaneum and astragalus. 



346 THE VERTEBRATE SKELETON. 

Of these the calcaneum is the fibulare, and the astragalus is 
generally regarded as the tibiale and intermedium fused 1 . 

Subclass I. ORNITHODELPHIA OR PROTOTHERIA. 

This sub-class contains only a single order, the Monotre- 
niata, and the following characteristics are equally applicable 
to the subclass and to the order. The vertebral centra have 
no epiphyses, and the odontoid process remains for a long time 
free from the centrum of the second vertebra. With the 
exception of the atlas of Echidna the cervical vertebrae are 
without zygapophyses. The cranial walls are smooth and 
rounded, and the sutures between the several bones early 
become completely obliterated as in birds. The mandible is a 
very slight structure, with no ascending ramus, and with the 
coronoid process (see p. 398) and angle rudimentary. The 
auditory ossicles show a low state of development. The tuber- 
cula of the ribs articulate with the sides of the centra of the 
thoracic vertebrae, not with the transverse processes. Some of 
the cervical ribs remain for a long time separate from the verte- 
brae. Well ossified sternal ribs occur. No true teeth are present 
in the adult. The young OrnitJiorhynchus has functional molar 
teeth, but in the adult their place is taken by horny plates. 
In the Echidnidae neither teeth nor horny plates occur. 

The coracoid (fig. 66, 3) is complete and well developed, 
and articulates with the sternum. A precoracoid (epicoracoid) 
occurs in front of the coracoid, and there is a large interclavicle 
(fig. 66, 6). The ridge on the scapula, corresponding to the 
spine of other mammals, is situated on the anterior border 
instead of in the middle of the outer surface. Epipubic bones 
are present. In the Echidnidae, but not in Ornithorhynchus'*, 

1 Baur, however, suggests (Anat. Am. vol. iv. 1889), that a tibial 
sesamoid found in Procavia, many rodents, edentates and Ornithorhyn- 
chns is a vestigial tibiale, and that the astragalus is the intermedium. 

2 This perforation of the acetabulum in Echidna is a secondary 
character occurring late in development, and consequently is not of 
phylogenetic importance. 



MAMMALIA. ORXITHODELPHIA. 



347 



the central portion of the acetabulum is unossified as in birds. 
The humerus has a prominent deltoid crest ; its ends are much 
expanded, and the distal end is pierced by an ent-epicondylar 




FIG. 66. YEXTRAL VIEW OF THE SHOULDER-GIRDLE AXD STERXUJC OF 
A DUCKBILL (O r nit Jwrhynchus paradox us) x f (after PARKER). 



1 and 2. scapula. 
3. coracoid. 

precoracoid (epicoracoid). 

glenoid cavity. 

interclavicle. 

clavicle. 



8. prestemnm. 

9. third segment of mesoster- 

num. 

sternal rib. 
intermediate rib. 
vertebral rib. 



10. 
11. 
12. 



4. 
5. 
6. 
7. 

foramen. The fibula has a broad proximal process resembling 
an olecranon. The limbs and their girdles bear a striking 
resemblance to those of some Theromorphous reptiles. 

The order Monotremata includes only two living families, 
the Echidnidae and Ornithorhynchidae. 



348 THE VERTEBRATE SKELETON. 

MESOZOIC MAMMALIA 1 . 

It will be well here to briefly refer to certain mammals 
of small size, the remains of which have been found in de- 
posits of Mesozoic age. In the great majority of cases they 
are known only by the lower jaw, or sometimes only by isolated 
teeth. A large number of them are commonly grouped 
together as the Multituberculata, and are sometimes, partly 
owing to the resemblance of their teeth to those of Ornitho- 
rhynchus, placed with the Prototheria, sometimes between the 
Prototheria and the Metatheria. They are characterised by 
having a single pair of large incisors in the lower jaw, and one 
large with one or two smaller incisors in each premaxilla. 
The lower canines are very small or altogether wanting. The 
incisors are separated by a diastema from the grinding teeth, 
which are sometimes (Tritylodon) characterised by the posses- 
sion of longitudinal rows of little tubercles separated by 
grooves, sometimes by having the premolars provided with 
high cutting edges, whose surfaces are obliquely grooved. 
Some of the Mesozoic mammals found associated with the 
Multituberculata, have however a dentition of an altogether 
different type, with at least three lower incisors, well developed 
canines and premolars, and numerous molars with peculiar 
three-cusped or tritubercular grinding surfaces. These mam- 
mals, one of the best known of which is Phascolotherium, are 
commonly separated from the Multituberculata, and are divided 
by Osborn into two groups, one allied to the Marsupials, and 
one to the Insectivores. The group showing Marsupial affinities 
is further subdivided into carnivorous, omnivorous, and herbi- 
vorous subgroups. The members of both groups commonly 

1 See E. Owen, "Monograph of the Fossil Mammalia of the Mesozoic 
Formation," Pal. Soc. Mon. 1871. 

H. F. Osborn, "Structure and Affinities of Mesozoic Mammals," 
J. of Philad. Acad. 1888, vol. ix. 

O. C. Marsh, "Jurassic Mammals," Amer. J. Sci. 1878 et seq. 



MAMMALIA. DIDELPHIA. 34)9 

have four premolars, and six to eight molars in each mandibular 
ramus. 

Subclass II. DIDELPHIA OR MKTATHERIA. 

This subclass, like the previous one, contains only a single 
order, viz. the Marsupialia 1 ; but the forms referable to it are 
far more numerous than in the case of the Monotremata. 

The integument is always furry, and the teeth are always 
differentiated into incisors, canines, premolars and molars. 
Except in Phascolomys, the number of incisors in the upper 
and lower jaws is never equal, and the number in the upper 
usually exceeds that in the lower jaw. There is no such 
regular succession and displacement of teeth as in most mam- 
mals. Sometimes the anterior teeth are diphyodont, and as a 
general rule the tooth commonly regarded as the last premolar 
is preceded by a milk tooth. The majority of the permanent 
teeth of most Marsupials are regarded as belonging to the milk 
series for two reasons, (1) they are developed from the more 
superficial tissues of the jaws, (2) a second set, the permanent 
teeth, begin to develop as outgrowths from them, but after 
wards become aborted 2 . 

The odontoid process at an early stage becomes fused with 
the centrum of the second cervical vertebra, and the number 
of thoraco-lumbar vertebrae is always nineteen. The skull has 
several characteristic features. The tympanic bone remains 
permanently distinct, and the anterior boundary of the tym- 
panic cavity is formed by the alisphenoid. The carotid canal 
perforates the basispheiioid, and the lachrymal canal opens 
either outside the orbit or at its margin. There are generally 
large vacuities in the palate. The angle qf the mandible is 
(except in Tarsipes) more or less inflected ; and as a rule the 
jugal furnishes part of the articular surface for the mandible. 

1 See Oldfield Thomas, Brit. Mus. Cat. of Marsupialia and Monotre- 
mata (1888). 

- W. Kukenthal, Anat. Am. vi. p. 364, 1891. C. Rose, Anat. Anz. 
vii. p. 639. 



350 THE VERTEBRATE SKELETON. 

There is no precoracoid (epicoracoid) or interclavicle, and the 
coracoid is reduced to form a mere process of the scapula, not 
coming near the sternum. 

Epipubic, or so-called marsupial bones 1 , nearly always 
occur, and a fourth pelvic element, the acetabular bone, is 
frequently developed. The fibula is always complete at its 
distal end, sometimes it is fused with the tibia, but often it is 
not only free but is capable of a rotatory movement on the 
tibia. This is the case in the families Phascolomyidae, Didel- 
phyidae, and Phalangeridae. 

The Marsupialia can be subdivided into two main groups, 
according to the character of the teeth : 

1. POLYPUOTODONTIA. 

In this group the incisors are small, subequal and nume- 
rous, not less than ^. The canines are larger than the 
incisors, and the molars have sharp cusps. The members of 
this group are all more or less carnivorous or insectivorous. 
The group includes the families Didelphyidae, Dasyuridae, 
Peramelidae, and Notoryctidae*. 

2. DlPROTODONTIA. 

In this group the incisors do not exceed f , and are usually 
Y, occasionally 1. The first upper and lower incisors are large 
and cutting. The lower canines are always small or absent, 
and so in most cases are the upper canines. The molars have 
bluntly tuberculated, or transversely ridged crowns. The 
group includes the families Phascolomyidae, Phalangeridae, 
Macropodidae, and Epanorthidae. 

1 These bones however have no connection with the marsupium, 
being nearly equally developed in both male and female. They are 
simply sesamoid bones forming ossifications in the inner tendon of the 
external oblique muscle, and are developed as supports for the abdominal 
wall. Very similar structures have been independently developed in 
various Amphibians, Reptiles and monodelphian Mammals. See W. Leche, 
Biol. Fin-en, in. p. 120. 

3 See H. Gadow, P. Z. S. 1892, p. 361. 



MAMMALIA. EDENTATA. 351 

Subclass III. MOXODELPHIA OR EUTHERIA. 

This great group -includes all the Mammalia except the 
orders Monotremata and Marsupialia. Coming to their 
general characteristics as in the Didelphia the odontoid 
process and cervical ribs early become fused with the centra 
which bear them, while the coracoid is reduced so as to form a 
mere process on the scapula, and there is no precoracoid (epi- 
coracoid), such as is found in Ornithodelphia. Clavicles may 
be present or absent : when fully developed they articulate 
with the sternum, usually directly, but occasionally, as in some 
Rodents and Insectivores, through the remains of the sternal 
end of the precoracoid. There is never any interclavicle in 
the adult, though sometimes traces of it occur during develop- 
ment. In the pelvis the acetabula are imperforatc ; and well- 
developed epipubic bones are never found in the adult, 
though traces of them occur in some Carnivores and foetal 
Ungulates. 

Order 1. EDENTATA '. 

Teeth are not, as the name of the order seems to imply, 
always wanting ; and sometimes they are very numerous. 
They are, however, always imperfect, and, with very few 
exceptions, are homodont and monophyodont. They have 
persistent pulps, and so grow indefinitely and are never rooted. 
In all living forms they are without enamel, consisting merely 
of dentine and cement, and are never found in the front part of 
the mouth in the situation occupied by the incisors of other 
mammals. These characters derived from the teeth are the 
only ones common to the various members of the order, 

1 See W. H. Flower, "On the Mutual Affinities of the Animals com- 
posing the order Edentata," P. Z. S. 1882, p. 358. For the fossil 
Edentates of N. America see E. Cope, Amer. Xatural. 1889; for those of 
S. America see various papers by F. Ameghino, H. Burmeister and R. 
Owen. Also T. H. Huxley, "On the Osteology of Glyptodon," Phil. 
Trans. 1865. 



352 THE VERTEBRATE SKELETON. 

which includes the living sloths, anteaters, armadillos, pangolins 
and aard varks, together with various extinct forms, chiefly 
found in beds of late tertiary age in both North and South 
America, the best known being the Megatheridae and Glypto- 
donts. 

Order 2. SiKENiA 1 . 

The skeleton of these animals has a general fish-like form, 
in correlation with their purely aquatic habits. The fore limbs 
have the form of paddles, but the number of phalanges is not 
increased beyond the normal. There are no external traces of 
hind limbs. 

The whole skeleton and especially the skull and ribs is 
remarkably massive and heavy. The dentition varies ; in the 
two living genera Manatus a.nd Halicore, incisor and molar 
teeth are present, in one extinct genus, Rhytina, teeth are 
entirely absent, while in another, Halitherium, the dentition 
is more decidedly heterodont than in living forms. In the 
two living genera the dentition is monophyodont, but in 
Halitherium the anterior grinding teeth are preceded by 
milk teeth. The tongue and anterior part of the palate and 
lower jaw are covered with roughened horny plates. The 
skull is noticeable for the size and backward position of the 
anterior nares, also for the absence or small size of the nasal 
bones. There is no union of certain of the vertebrae to form 
a sacrum, and in living forms the centra are not terminated by 
well-formed epiphyses 2 . 

The cervical vertebrae are much compressed, but they are 
never ankylosed together. In Manatus there are only six 
cervical vertebrae. The caudal vertebrae have well-developed 
chevron bones. The humerus is distinctly articulated to the 

1 See J. F. Brandt, Symbolae Sirenologicae, St Petersburg, 1846, 1861, 
1868. 

2 Epiphyses are fully developed in Halitherium, and traces occur in 
Manatut. 



MAMMALIA. CETACEA. 353 

radius and ulna, and these two bones are about equally de- 
veloped, and are often fused together. There are no clavicles, 
and the pelvis is vestigial, consisting of a pair of somewhat 
cylindrical bones suspended at some distance from the ver- 
tebral column. In living forms there is no trace of a posterior 
limb, but in Halitherium there is a vestigial femur connected 
with each half of the pelvis. 

Order 3. CETACEA 1 . 

In these mammals the general form is more fish-like than is 
the case even in the Sirenia. The skin is generally almost 
completely naked, but hairs are sometimes present in the neigh- 
bourhood of the mouth, especially in the foetus. In some 
Odontoceti vestiges of dermal ossicles have been described, and 
in Zeuglodon the back was probably protected by dermal plates. 
The anterior limbs have the form of flattened paddles, showing 
no trace of nails, the posterior limb bones are quite vestigial 
or absent, and there is never any external sign of the limb. 
Teeth are always present at some period of the life history, but 
in the whalebone whales they are only present during foetal 
life, their place in the adult animal being taken by horny 
plates of baleen. In all living forms the teeth are simple 
and uniform structures without enamel ; they have single 
roots, and the alveoli in which they are imbedded are often 
incompletely separated from one another. As in some forms 
traces of a replacing dentition have been described, it has 
been concluded that the functional teeth of Cetacea belong to 
the milk dentition. 

The texture of the bones is spongy. The cervical vertebrae 
are very short, and though originally seven in numljer, are in 
many forms completely fused, forming one solid mass (fig. 67). 
The odontoid process of the axis is short and blunt, or may 

1 See P. J. van Beneden and P. Gervais, Osteographie des Cetaces, 
186980. 

R. 23 



354 



THE VERTEBRATE SKELETON. 



be completely wanting. The lumbar and caudal vertebrae are 
large and numerous, and as zygapophyses are absent, are very 



--4 




."5 



FIG. 67. CERVICAL VERTEBRAE OF A CA'ING WHALE (Globicephalus 
melas) x J. (Camb. Mus.) 



1. centrum of seventh cervical 

vertebra. 

2. neural arch of seventh cer- 

vical vertebra. 

3. transverse process of atlas. 



4. foramen for exit of first spinal 

nerve. 

5. transverse process of axis. 

6. fused neural spines of atlas 

and axis. 



freely movable on one another ; zygapophyses are also absent 
from the posterior thoracic vertebrae. The lumbar vertebrae 
are sometimes more numerous than the thoracic. The epi- 
physes are very distinct, and do not unite with the centra till 
the animal is quite adult. None of the vertebrae are united 
to form a sacrum, but the caudal vertebrae have large chevron 
bones. 

The skull is peculiarly modified ; the bones forming the 
occipital segment show a specially strong development, and 
the cranial cavity is short, high, and almost spherical. The 
supra-occipital is very large and rises up to meet the f rentals. 



MAMMALIA. CETACEA. 355 

thus with the interparietal completely separating the parietals 
from one another. 

The frontals are expanded, forming large bony plates, 
which roof over the orbits. The zygornatic process of the 
squainosal is extremely large and extends forwards to meet 
the supra-orbital process of the frontal; the zygomatic process 
of the jugal is on the contrary very slender. The face is 
drawn out into a long rostrum, formed of the maxillae and 
premaxillae surrounding the vomer and the mesethmoid 
cartilage. The maxillae are specially large, and extend back- 
wards so as to partially overlap the frontals. The nasals are 
always small, and the anterior nares open upwards between 
the cranium and rostrum. The periotics are loosely connected 
with the other bones of the skull and the tympanics are com- 
monly large and dense. The mandible has hardly any coronoid 
process, and the condyles are at its posterior end. 

There are no clavicles, but the scapula and humerus are 
well developed. The humerus moves freely in the glenoid 
cavity, but all the other articulations of the anterior limb are 
imperfect ; the various bones have flattened ends, and are 
connected with one another by fibrous tissue, which allows of 
hardly any movement. Frequently the carpus is imperfectly 
ossified. 

The number of digits in the manus is generally five, some- 
times four, and when there are four digits it is the third and 
not the first that is suppressed. The number of phalanges 
in the second and third digits almost always exceeds that 
which is normal in mammals, and the phalanges are also 
remarkable for having epiphyses at both ends. The pelvis is 
represented by two small bones which lie suspended horizon- 
tally at some distance below the vertebral column ; in some 
cases vestiges of the skeleton of the hind limb are attached to 
them. 

The Cetacea are divided into three suborders. 

232 



356 THE VERTEBRATE SKELETON. 

Suborder (1). ARCHAEOCETI. 

The members of this group are extinct; they differ from 
all living Cetacea in having the dentition heterodont and in 
the fact that the back was probably protected by dermal 
plates. The skull is elongated and depressed, and the brain 
cavity is very small. The temporal fossae are large, and 
there is a strong sagittal crest. The nasals and premaxillae 
are a good deal larger than they are in living Cetacea, and 
the anterior nares are usually far forward. The cervical ver- 
tebrae are not fused with one another, and the lumbar 
vertebrae are unusually elongated. 

The limbs are very imperfectly known, but while the 
humerus is much longer than in modern Cetaceans, it is 
nevertheless flattened distally, indicating that the limb was 
paddle-like, and that there was scarcely any free movement 
between the fore-arm and upper arm. 

The best known genus is Zeuglodon, which is found in 
beds of Eocene age in various parts of Europe, and in Alabama. 

Suborder (2). MYSTACOCETI or BALAENOIDEA. 

These are the Whalebone Whales or True Whales. 

Calcined teeth representing the milk dentition occur in the 
foetus, but the teeth are never functional, and always dis- 
appear before the close of foetal life. There is a definite 
though small olfactory fossa. The palate is provided with 
plates of baleen or whalebone. The skull is symmetrical, and 
is extremely large in proportion to the body. The nasals are 
moderately well developed, and the maxillae do not overlap 
the orbital processes of the frontals. The lachrymals are small 
and distinct from the jugals. The tympanics are ankylosed 
to the periotics, and the rami of the mandible do not meet in 
a true symphysis. The ribs articulate only with the transverse 
processes, and the- capitula are absent or imperfectly deve- 
loped. Only one pair of ribs meets the sternum, which is 
composed of a single piece. 



MAMMALIA. CETACEA. 357 

The group includes among others the Right whale (Bataena), 
Humpbacked whale (Megaptera), and Rorqual (Balaenoptera). 

Suborder (3). ODONTOCETI. 

Teeth always exist after birth and baleen is never present. 
The teeth are generally numerous, but are sometimes few and 
deciduous ; the dentition is homodont (except in Squalodori). 
The dorsal surface of the skull is somewhat asymmetrical, 
there is no trace of an olfactory fossa, the nasals are quite 
rudimentary, and the hind ends of the maxillae cover part of 
the frontals ; in all these respects the skull differs from that 
of the Mystacoceti. The lachrymal may either be united to 
the jugal or may be large and distinct. The tympanic is 
not ankylosed to the periotic. The rami of the mandible are 
nearly straight and become united in a long symphysis. Some 
of the ribs have well developed capitula articulating with the 
vertebral centra. The sternum is almost always composed of 
several pieces as in other mammals, and several pairs of ribs 
are connected with it. There are always five digits to the 
manus, though the first and fifth are usually very little 
developed. 

The suborder includes the Sperm Whale (Physeter), Xar- 
whal (Manodoti), Dolphin (Delphinus), Porpoise (Phocoena), 
and many other living forms as well as the extinct Squalodon 
which differs from the other members of the suborder in its 
heterodont dentition. 

Order 4. UNGULATA. 

This order includes a great and somewhat' heterogeneous 
group of animals, a large proportion of which are extinct. 
They all (except certain extinct forms) agree in having the 
ends of the digits either encased in hoofs or provided with 
broad flat nails. The teeth are markedly heterodont and 
diphyodont, and the molars have broad crowns with tubercu- 
lated or ridged surfaces. Clavicles are never present in the 



358 THE VERTEBRATE SKELETON. 

adult except in a few generalised extinct forms such as Typo- 
therium, and it is only recently that vestigial clavicles have 
been discovered in the embryo 1 . The scaphoid and lunar are 
always distinct. 

The order Ungulata may be subdivided into two main 
groups, Ungulata vera and Subungulata. 

Section I. UNGULATA VERA 2 . 

The cervical vertebrae except the atlas are generally opis- 
thocoelous. The feet are never plantigrade 3 . In all the 
living and the great majority of the extinct forms the digits 
do not exceed four, the first being suppressed. In the carpus 
the os magnum articulates freely with the scaphoid, and is 
separated from the cuneiform by the lunar and unciform. In 
the tarsus the cuboid articulates with the astragalus as well as 
with the calcaneum, and the proximal surface of the astra- 
galus is marked by a pulley-like groove. All the bones of 
the carpus and tarsus strongly interlock. These characters 
with regard to the carpus and tarsus do not hold in Macrau- 
chenia and its allies. The humerus never has an ent-epicon- 
dylar foramen. 

The group is divided into two very distinct suborders: 

Suborder (1). ARTIODACTYLA. 

The Artiodactyla have a number of well marked charac- 
ters, one of the most obvious being the fact that many of the 
most characteristic forms have large paired outgrowths on the 
frontal bones. These may be (1) solid deciduous bony antlers, 
or (2) more or less hollow bony outgrowths which are sheathed 
with permanently growing horn. 

1 H. Wincza, Morphol. Jahrb. xvi., p. 647. 

2 See M. Pavlow, "Etudes sur 1'histoire paleontologique des Ongules." 
Bull. Soc. Moscou, 18871890. 

3 In a plantigrade animal the whole of the foot is placed on the 
ground in walking. A digitigrade animal places only its toes on the 
ground. An intermediate condition is distinguished by the term xnl>- 
plantigrade. 



MAMMALIA. ARTIODACTYLA. 359 

. The premolar and molar teeth are usually dissimilar, the 
premolars being one-lobed and the molars two-lobed; the last 
lower molar of both the milk and permanent dentitions is 
almost always three-lobed. 

The grinding surfaces of the molar teeth have a tendency 
to assume one of two forms. In the Pigs and their allies the 
crowns are bunodont 1 , while in the more highly specialised 
Ruminants the crowns are selenodont 1 . The nasals are not 
expanded posteriorly, and there is no alisphenoid canal*. The 
thoraco-lumbar vertebrae are always nineteen. The symphysis 
of the ischia and pubes is very elongated, and the femur has 
no third trochanter. The limbs never have more than four 
digits, and are symmetrical about a line drawn between the 
third and fourth digits ; the digits, on the other hand, are 
never symmetrical in themselves. The astragalus has pulley- 
like surfaces both proximally and distally, and articulates with 
the navicular and cuboid by two nearly equal facets. The 
calcaneum articulates with the lower end of the fibula when 
that bone is fully developed. 

In the Artiodactyla are included the following living 
groups : 

a. Suina. Pigs and Hippopotami. 

b. Tylopoda. Camels and Llamas. 

c. Tragulina. Chevrotains. 

d. Ruminantia or Pecora. Deer, giraffes, oxen, sheep 
and antelopes. 

Suborder (2). PERISSODACTYLA S . 

In this group there are never any bony outgrowths from 
the frontals. The grinding teeth form a continuous series, 
the posterior premolars resembling the molars in complexity, 
and the last lower molar generally has no third lobe. The 

1 See p. 34o. - See p. 401. 

3 SeeE. D. Cope, "The Perissodactyla," Amer. Natural, 1887. 



360 THE VERTEBRATE SKELETON. 

cervical vertebrae with the exception of the atlas almost 
always have markedly opisthocoelous centra, but in Macrau- 
chenia they are flat. The nasals are expanded posteriorly, and 
an alisphenoid canal is present. The thoraco-lumbar vertebrae 
are never less than twenty-two in number and are usually 
twenty-three. The femur has a third trochanter (except in 
Ckalicotherium). The third digit of the nianus and pes is 
symmetrical in itself, and larger than the others, and in some 
cases the other digits are quite vestigial. The number of the 
digits of the pes is always odd. The astragalus is abruptly 
truncated distally, and the facet by which it articulates with 
the cuboid, is much smaller than that by which it articulates 
with the navicular. The calcaneum does not articulate with 
the fibula, except in Macrauchenia. The group includes many 
extinct forms, and the living families of the Tapirs, Horses 
and Asses, and Rhinoceroses. 



Section II. SUBUNGULATA. 

In this group is placed a heterogeneous collection of 
animals, the great majority of which are extinct. There is 
really no characteristic which is common to them all, and 
which serves to distinguish them as a group from the Ungulata 
vera. But the most distinctive character common to the 
greatest number of them is to be found in the carpus, whose 
bones in most cases retain their primitive relation to one 
another, the os magnum articulating with the lunar and some- 
times just meeting the cuneiform, but in living forms at any 
rate not articulating with the scaphoid. The feet frequently 
have five functional digits, and may be plantigrade. The 
proximal surface of the astragalus is generally flattened in- 
stead of being pulley-like as in Ungulata vera. 



MAMMALIA. SUBUNGULATA. 361 

Suborder (1). TOXODONTIA. 

This suborder includes some very aberrant extinct South 
American ungulates, which have characters recalling the 
Proboscidea, both groups of Ungulata vera,' and the Rodentia. 
The limbs are subplantigrade or digitigrade, and the digits 
are three, rarely five, in number, the third being most 
developed. The carpus resembles that of the Ungulata vera, 
in that the bones interlock and the magnum articulates with 
the scaphoid. In the tarsus, however, the bones do not 
interlock. The astragalus has a pulley-like proximal sur- 
face (except in Astrapotherium, in which it is flat), and 
articulates only with the navicular, not meeting the cuboid. 
The calcaneum has a large facet for articulation with the 
fibula, as in Artiodactyla. There is no alisphenoid canal, and 
the orbit is confluent with the temporal fossa. Some of the 
forms (e.g. Nesodori) referred to this group have the typical 
mammalian series of forty-four teeth, but in others the canines 
are undeveloped. In Toxodon all the cheek-teeth have persist- 
ent pulps, while in Nesodon and Astrapotherium they are rooted. 
A clavicle is sometimes present (Typotherium), and the femur 
sometimes has a third trochanter (Typotherium and Astra- 
potherium}, sometimes is without one (Toxodon). 

The remains of these curious Ungulates have been found 
in beds of late Tertiary age in South America. 

Suborder (2). CONDYLARTHRA'. 

This group includes some comparatively small extinct 
ungulates, which are best known from the Lower Eocene of 
Wyoming, though their remains have also been found in 
deposits of similar age in France and Switzerland. Their 

1 See E. D. Cope, "The Condylarthra," Amer. Natural., 1884, and 
"Synopsis of the Vertebrates of the Puerco series," Tr. Amer. Phil. Soc., 
1888. 0. C. Marsh, "A new order of extinct Eocene Mammals (Meso- 
dactyla)," Amer. J. Sci., 1892. 



362 THE VERTEBRATE SKELETON. 

characters are little specialised, and they show relationship on 
the one hand to the Ungulata vera and on the other to the 
Hyracoidea. They also have characters allying them to the 
Carnivora. They generally have the typical mammalian 
series of forty-four teeth, the molars being brachydont and 
generally bunodont. The premolars are more simple than the 
molars. The limbs are plantigrade, and have five digits with 
rather pointed ungual phalanges. The os magnum, as in living 
Subungulates, articulates with the lunar, not reaching the 
scaphoid. The astragalus has an elongated neck, a pulley-like 
proximal and a convex distal articular surface, and does not 
articulate with the cuboid. The humerus has an ent-epicondylar 
foramen, and the femur has a third trochanter. The best 
known genus is Phenacodus ; it is perhaps the most primitive 
ungulate whose skeleton is thoroughly well known, and is of 
special interest from the fact that it is regarded as the lowest 
stage in the evolutionary series of the horse. Its remains 
are found in the Lower Eocene of Wyoming. 

Suborder (3). HYRACOIDEA 1 . 

This group of animals is very isolated, having no very close 
allies, either living or extinct. The digits are provided with 
flat nails, except the second digit of the pes, which is clawed. 
Canine teeth are absent, and the dental formula is usually 

.10 4 3 

given as i ^, c ^, pm -, m ~. Ihe upper incisors are long 

and curved, and have persistent pulps as in Rodents ; their 
terminations are, however, pointed, not chisel-shaped, as in 
Rodents. The lower incisors have pectinated edges. The 
grinding teeth have a pattern much like that in Rhinoceros, 
In the skull (fig. 83) the postorbital processes of the frontal 
and jugal almost or quite meet. The jugal forms part of the 

1 See 0. Thomas, "On the species of Hyracoidea," P. Z. S., 1892, 
p. 50. 



MAMMALIA. SUBUNGULATA. 363 

glenoid cavity for articulation with the mandible, and also 
extends forwards so as to meet the lachrymal. There is an 
alisphenoid canal. There are as many as twenty-one or twenty- 
two thoracic vertebrae, and the number of thoraco- lumbar 
vertebrae reaches twenty-eight or thirty. There are no clavi- 
cles, and the scapula has no acromion ; the coracoid process 
is, however, well developed. The ulna is complete. In the 
nianus the second, third and fourth digits are approximately 
equal in size, the fifth is smaller, and the first is vestigial. 
The femur has a slight ridge representing the third trochanter. 
The fibula is complete, but is generally fused with the tibia 
proximally. There is a complicated articulation between the 
tibia and astragalus, which has a pulley-like proximal surface. 
In the pes the three middle digits are well developed, but there 
is no trace of a hallux, and the fifth digit is represented only 
by a vestigial metatarsal. 

The only representatives of the suborder are some small 
animals belonging to the genus Procavia (Hyrax), which is 
found in Africa and Syria ; some of the species are by many 
authors placed in a distinct genus Dendrohyrax. 

Suborder (4). AMBLYPODA'. 

This suborder includes a number of primitive extinct 
Ungulates, many of which are of great size. Their most 
distinguishing characteristics are afforded by the extremities. 
In the carpus the bones interlock a little more than is the case 
in most Subungulata, and the corner of the os magnum reaches 
the scaphoid, while the lunar articulates partially with both 
magnum and unciform, instead of only with the magnum. 
In the tarsus the cuboid articulates with both the calcaneum 
and the astragalus, which is remarkably flat. The manus and 
pes are short, nearly or quite plantigrade, and have the full 
number of digits. The cranial cavity is singularly small. 

1 See E. D. Cope, "The Amblypoda," Amer. KaturaL, 1884 and 1885. 



364 THE VERTEBRATE SKELETON. 

Canine teeth are present in both jaws, and the grinding teeth 
have short crowns, marked by V-shaped ridges. The pelvis is 
large, the ilia are placed vertically, and the ischia do not take 
part in the ventral syinphysis. 

The best known animals belonging to this suborder are the 
Uintatheriidae (Dinocerata) 1 , found in the Upper Eocene of 
Wyoming. They are as large as elephants, and are charac- 
terised by the long narroAv skull drawn out into three pairs 
of rounded protuberances, by the strong occipital crest, and 
by the very large upper canines. 

Suborder (5). PROBOSCIDEA. 

This suborder includes the largest of land mammals, the 
Elephants, and certain of their extinct allies. The limbs are 
strong, and are vertically placed ; the proximal segment is the 
longest, and the manus and pes are pentedactylate and sub- 
plantigrade. The digits are all enclosed in a common integu- 
ment, and each is provided with a broad hoof. The vertebral 
centra are much flattened and compressed, especially in the cer- 
vical region. The number of thoracic vertebrae is very great, 
reaching twenty. The skull (figs. 96 and 97) is extremely large, 
this being due to the great development of air cells, which 
takes place in nearly all the bones of the adult skull. In the 
young skull there are hardly any air cells, and the growth of 
the cranial cavity does not by any means keep pace with the 
growth of the skull in general. The supra-occipital is very 
large, and forms a considerable part of the roof of the skull. 
The nasals and jugals are short, and the premaxillae very 
large. The rami of the mandible meet in a long symphysis, and 
the ascending portion is very high. Canine teeth are absent, 
and the incisors have the form of ever-growing tusks composed 
mainly of dentine ; in living forms they are present in the 
upper jaw only. The grinding teeth are large, and in living 

1 See 0. C. Marsh, "The Dinocerata," U. S. Geol. Survey, 1884, 
vol. x. 



MAMMALIA. RODENTIA. 365 

forms have a very complex structure and mode of succession. 
In some of the extinct forms, such as Mastodon and especially 
Dinotherium, the teeth are much more simple. In every case 
the teeth have the same general structure, consisting of a 
.series of ridges of dentine, coated with enamel. In the more 
specialised forms the valleys between the ridges are filled up 
with cement. The acromion of the scapula has a recurved 
process, similar to that often found in rodents. Clavicles are 
absent. The radius and ulna are not ankylosed, but are 
incapable of any rotatory movement. All the bones of the 
extremities are very short and thick ; the scaphoid articulates 
regularly with the trapezoid and the lunar with the magnum. 
The ilia are vertically placed, and are very much expanded ; 
the ischia and pubes are small, and form a short symphysis. 
The femur has no third trochanter, and the tibia and fibula 
are distinct. The fibula articulates with the calcaneum, and 
the astragalus is very flat. 

Here brief reference may be made to the TILLODOXTIA ', a 
group of extinct mammals found in the Eocene beds of both 
Europe and North America. They seem to connect together 
the Ungulata, Rodentia, and Carnivura. 

The skull resembles that of bears, but the grinding teeth 
are of Ungulate type, while the second incisors resemble those 
of rodents, and have persistent pulps. The femur has a third 
trochanter, and the feet resemble those of bears in being 
plantigrade and having pointed ungual phalanges, differing, 
however, in having the scaphoid and lunar distinct. 

Order 5. RODENTIA. 

The Rodents form a very large and well-defined group of 

mammals easily distinguishable by their peculiar dentition. 

Canines are absent, and the incisors are very large and curved, 

growing from persistent pulps. They are rectangular in section 

1 See 0. C. Marsh, Amer. J. Sci., 1875 and 1876. 



366 THE VERTEBRATE SKELETON. 

and are much more thickly coated with enamel on their 
anterior face than elsewhere ; consequently, as they wear down 
they acquire and retain a chisel-shaped (scalpriform) edge. 
There is never -more than one pair of incisors in the mandible, 
and except in the Hares and Rabbits, there is similarly only a 
single pair in the upper jaw. These animals are, too, the only 
rodents which have well developed deciduous incisors. There 
is always a long diastema separating the incisors from the 
grinding teeth. The grinding teeth, which are arranged in a 
continuous series, vary in number from two to six in the upper 
jaw, and from two to five in the lower jaw. The number of 
premolars is always below the normal, often they are altogether 
wanting, but generally they are T . Sometimes the grinding 
teeth form roots, sometimes they grow persistently. 

The premaxillae are always large, and the orbits always com- 
municate freely with the temporal fossae. The condyle of the 
mandible is elongated from before backwards, and owing to 
the absence of a postglenoid process to the squamosal, a back- 
ward and forward motion of the jaw can take place. The 
zygomatic arch is complete, but the jugal is short and only 
forms the middle of it. The palate is small, being some- 
times, as in the hares, narrowed from before backwards, 
sometimes as in the mole-rats (Bathyerginae) narrowed trans- 
versely. 

The thoraco-lumbar vertebrae are usually nineteen in 
number. Clavicles are generally present, and the acromion 
of the scapula is commonly very long. The feet are as a rule 
plantigrade, and provided with five clawed digits. 

There are two main groups of Rodentia ; the Duplici- 
dentata, or Hares and Rabbits, which have two pairs of upper 
incisors, whose enamel extends round to the posterior surface ; 
and the Simplicidentata, in which there is only a single pair 
of upper incisors, whose enamel is confined to the anterior 
surface. This group includes all the Rodents except the 
Hares and Rabbits. 






MAMMALIA. CARXIVORA. 367 



Order 6. CARXIVORA. 

The living Carnivora form a natural and well-marked 
group, but as is the case with so many other groups of 
animals, when their extinct allies are included, it becomes 
impossible to readily define them. 

The manus and pes never have less than four well-developed 
digits, and these are nearly always provided with more or less 
pointed nails, generally with definite claws. The hallux and 
pollex are never opposable. The dentition is diphyodont and 
markedly heterodont. The teeth are always rooted, except 
in the case of the canines of the Walrus. The incisors are 
generally ^, and are comparatively small, while the canines 
are large, pointed, and slightly recurved. The cheek teeth are 
variable, and are generally more or less compressed and 
pointed ; sometimes their crowns are flattened and tuber- 
culated, but they are never divided into lobes by deep infoldings 
of enamel. The squamosal is drawn out into a postglenoid 
process, and the mandible has a large coronoid process. The 
condyle of the mandible is transversely elongated, and the 
glenoid fossa is very deep; in consequence of this arrangement 
the mandible can perform an up and down movement only, 
any rotatory or back and fore movement being impossible. 
The jugal is large, and the zygomatic arch generally strong, 
while the orbit and temporal fossa are in most cases completely 
confluent. The scapula has a large spine. The clavicle is 
never complete and is often absent, this forming an important 
distinction between the skeleton of a Carnivore and of any 
Insectivore except Potamogah. The humerus often has an 
ent-epicondylar foramen, and the radius and ulna, tibia and 
fibula are always separate. The manus is often capable of the 
movements of pronation and supination, and the scaphoid, 
lunar and centrale are in living forms always united together. 

The order Carnivora 'includes three suborders. 



368 THE VERTEBRATE SKELETON. 

Suborder (1). CKEODONTA'. 

This suborder contains a number of extinct Carnivora, 
which present very generalised characters. 

The cranial cavity is very small ; and the fourth upper pre- 
molar and first lower molar are not differentiated as carnassial 
teeth 2 , as they are in modern Garni vora. The Creodonta also 
differ from modern Carnivora in the fact that the scaphoid and 
lunar are usually separate, and that the femur has a third 
trochanter. The feet are plantigrade. 

They resemble the Condylarthra, another very generalised 
group, in having an ent-epicondylar foramen. 

They occurred throughout the Tertiary period in both 
Europe and North America, and have also been found in India. 
One of the best known genera is Hyaenodon. 

Suborder (2). CARNIVORA VERA or FISSIPEDIA. 

The skeleton is mainly adapted for a terrestrial mode of 
life, and the hind limbs have the normal mammalian position. 
In almost every case the number of incisors is . Each jaw 
always has one specially modified carnassial or sectorial tooth 
which bites like a scissors blade against a corresponding tooth 
in the other jaw. In front of it the teeth are always more 
or less pointed, while behind it they are more or less broadened 
and tuberculated. In the manus the first digit, and in the 
pes the first and fifth digits are never longer than the rest, 
and the digits of both limbs are almost invariably clawed. 
Some forms are plantigrade, some digitigrade, some sub- 
plantigrade. The group includes all the ordinary terrestrial 
Carnivora, and is divided into three sections : 

1 E. D. Cope, "The Creodonta," Amer. Natural,, 1884. W. B. Scott, 
"Revision of the N. American Creodonta," P.. Ac. Philad., 1892. 

2 See next paragraph. 



MAMMALIA. PINNIPEDIA. 369 

^luroidea 1 , including the cats, civets, hyaenas, and allied 
forms. 

Cynoidea, including the dog tribe. 

Arctoidea, including the bears, raccoons, weasels, and allied 
forms. 

Suborder (3). PINXIPEDIA*. 

In this suborder the limbs are greatly modified and adapted 
for a more or less purely aquatic life, the proximal and middle 
segments of the limbs are shortened, while the distal segment, 
especially in the leg, is much elongated and expanded. There are 
always five well-developed digits to each limb, and in the pes the 
first and fifth digits are generally larger than the others. The 
digits generaDy bear straight nails instead of claws, but even 
nails are sometimes absent. There is no carnassial tooth, and 
the teeth in other ways differ considerably from those of Carni- 
vora vera. The incisors are always fewer than f ; while the 
cheek teeth generally consist of four premolars and one molar, 
all of very uniform character, being compressed with conical 
crowns, and never more than two roots. 

The suborder includes three families Otariidae (Eared 
Seals), Trichechidae (Walrus), and Phocidae (Seals). 

Order 7. I^9ECTivoRA 3 . 

This order contains a large number of small generally ter- 
restrial mammals. The limbs are plantigrade or subplantigrade, 
and are generally pentedactylate. All the digits are armed 
with claws, and the pollex and hallux are not opposable. The 
teeth are diphyodont, heterodont, and rooted. The cheek teeth 

1 St G. Mivart, The Cat, London, 1881. 

2 St G. Mivart, P. Z. S., 1885. 

3 St G. Mivart, "On the Osteology of Insectivora," /. A not. Physiol. 
norm, path., 1867 and 1868, and P. Z. S., 1871. G. E. Dobson, Monograph 
of the Insectivora, London, 1882 90. 

R. 24 



370 THE VERTEBRATE SKELETON. 

have tuberculated crowns, and there are never less than two 
pairs of incisors in the mandible ; often the incisors, canines, 
and premolars are not clearly differentiated from one another, 
and special carnassial teeth are never found. The cranial cavity 
is small, and the facial part of the skull is generally much 
developed ; often the zygomatic arch is incomplete. Clavicles 
are well developed (except in Potamogale), and the humerus 
generally has an ent-epicondylar foramen. The femur fre- 
quently has a ridge representing the third trochanter. There 
are two suborders : 

Suborder (1). DERMOPTERA. 

This suborder includes only a very aberrant arboreal genus 
GaleopiihecuSj remarkable for its greatly elongated limb bones, 
and peculiar dentition. The incisors of the lower jaw are 
deeply pectinated or divided by several vertical fissures, the 
canines and outer upper incisors have two roots. Ossified 
intercentra occur in the thoraco-lumbar region of the vertebral 
column. 

Suborder (2). INSECTIVORA VERA. 

This suborder includes all the ordinary Insectivora, such as 
moles, shrews and hedgehogs. The upper and lower incisors 
are conical, not pectinated. 

Order 8. CniROPTERA 1 . 

This order is perhaps the best marked and most easily 
defined of all the orders of mammals. The anterior limbs 
form true wings and the whole skeleton is modified in relation 
to flight. 

The anterior limbs are vastly larger than the posterior ; 
for all the bones except the carpals are much elongated, and 

1 See G-. E. Dobson, Jirit. Mux. Catalogue of Chiroptera, 1878. See 
also other papers by the same author and by Oldfield Thomas. 



MAMMALIA. CHIROPTERA. 37 1 

this applies specially to the phalanges of all the digits except 
the pollex. 

The pollex is clawed and so is sometimes the second digit ; 
the other digits of the manus are without nails or claws. The 
teeth are divisible into the four usual types and the series 

21 33 

never exceeds i ^ c -= pm 5 m - x 2, total 38. The milk 
o 1 o o 

teeth are quite unlike the permanent teeth. The orbit is not 
divided by bone from the temporal fossa. The vertebral 
column is short, and in old animals the trunk vertebrae 
have a tendency to become partially fused together. The 
cervical vertebrae are remarkably wide, and the development 
of spinous processes is everywhere slight. The presternum 
has a prominent keel for the attachment of the pectoral muscles. 
The clavicles are very long and strong, and the scapula has a 
long spine and coracoid process. The ulna is vestigial, con- 
sisting only of a proximal end ankylosed to the radius. All 
the carpals of the proximal row the scaphoid, lunar and 
cuneiform are united, forming a single bone. The pelvis is 
very weak and narrow, and only in the Rhinolophidae do the 
pubes meet in a symphysis. The anterior caudal vertebrae are 
frequently united to the ischia. The fibula is generally ves- 
tigial, and the knee joint is directed backwards instead of 
forwards. The pes has five slender clawed digits, and the 
calcaneum is often drawn out into a spur which helps 
to support the membrane connecting the hind limbs with the 
tail. 

There are two suborders of Chiroptera : 

1. The MEGACHIBOPTERA or Flying foxes, which almost 
always have smooth crowns to the molar teeth, and the second 
digit of the manus clawed. 

2. The MICROCHIROPTERA including all the ordinary bats 
which have cusped molar teeth, and the second digit of the 
manus clawless. 

242 



372 THE VERTEBRATE SKELETON. 

Order 9. PRIMATES. 

The dentition is diphyodont and heterodont, the incisors 
generally number , and the molars, except in the Hapalidae 
(Marmosets), are . The cheek teeth are adapted for grind- 
ing, and the molars are more complex than the premolars. 
A process from the jugal meets the postorbital process of the 
frontal completing the postorbital bar. 

The clavicle is well developed, and the radius and ulna 
are never united. The scaphoid and lunar of the carpus, 
and commonly also the centrale, remain distinct from one 
another. As a rule both manus and pes have five digits, 
but the pollex may be vestigial. The pollex is opposable to 
the other digits, and so is the hallux except in Man ; the 
digits are almost always provided with flat nails. The hu- 
merus has no ent-epicondylar foramen and the femur has no 
third trochanter. 

The order Primates is divisible into two suborders : 

Suborder (1). LEMUROIDEA. 

The skull has the orbit communicating freely with the 
temporal fossa beneath the postorbital bar (except in Tar- 
sius). The lachrymal foramen is external to the margin of 
the orbit. Both pollex and hallux are well developed. In 
the pes the second digit is terminated by a long pointed claw, 
and so is also the third in Tarsius. The lumbar region of 
the vertebral column is long, sometimes including as many as 
nine vertebrae. Besides the Lemurs the group includes the 
aberrant Tarsius and Chiromys. 

Suborder (2). ANTHROPOIDBA. 

The skull has the orbit almost completely shut off from 
the temporal fossa, and the lachrymal foramen is situated 
within the orbit. The pollex is sometimes vestigial or absent. 



MAMMALIA. PRIMATES. 373 

The second digit of the pes has a flattened nail except in the 
Hapalidae, in which all the digits of the pes except the hallux 
are clawed. 

The Anthropoidea are divided into five families : 

1. Hapalidae or Marmosets. 

2. Cebidae or American Monkeys. 

3. Cercopithecidae or Old World Monkeys. 

4. Simiidae or Anthropoid Apes. 

5. Hominidae or Men. 



CHAPTER XXL 
THE SKELETON OP THE DOG 1 (Canis familiaris). 

I. EXOSKELETON. 

The exoskeleton of the dog includes three sets of structures : 
1. hairs, 2. claws, 3. teeth. Hairs and claws are epidermal 
exoskeletal structures, while teeth are partly of dermal, and 
partly of epidermal origin. 

1. Hairs are delicate epidermal structures which grow 
imbedded in little pits or follicles in the dermis. Specially 
large hairs forming the vibrissae or whiskers grow attached 
to the upper lip. 

2. Claws are horny epidermal sheaths, one of which fits 
on to the pointed distal phalanx of each digit. They are 
sharply curved structures, and being in the dog non-retractile, 
their points are commonly much blunted by friction with the 
ground. The claws of the pollex, and of the hallux when it is 
present, however do not meet the ground, and therefore remain 
comparatively sharp. 

3. Teeth 2 . Although as regards their mode of origin, 
teeth are purely exoskeletal or tegumentary structures, they 

1 W. Ellenberger and H. Baum, Anatomic des Hundes, Berlin, 1891. 

2 T. H. Huxley, "Dental and cranial characters of the Canidae, " 
P. Z. S. 1880. 



THE SKELETON OF THE DOG. THE TEETH. 



375 



become so intimately connected with the skull that they appear 
to l>elong to the endoskeleton. 

Each tooth, as has been already described, consists of three 
distinct tissues, dentine and cement of dermal origin, and 
enamel of epidermal origin. 




FIG. 68. DENTITION OF A DOG (Canis familiaris) x i. (Camb. Mus.) 
j 2. second incisor. pm 1, pm 4. first and fourth pre- 



c. canine. 



molars. 
TO 1. first molar. 



The teeth of the dog (fig. 68) form a regular series arranged 
along the margins of both upper and lower jaws, and imbedded 
in pits or alveoli of the maxillae, premaxillae, and mandibles. 



376 THE VERTEBRATE SKELETON. 

They are all fixed in the bone by tapering roots, and none of 
them grow from persistent pulps. 

They are divisible into four distinct groups, the incisors, 
canines, premolars and molars. There are three incisors, 
one canine and four premolars on each side of each jaw. 
But while there are three molars on each side of the lower 
jaw, the last is wanting in the upper jaw. The dentition of 
the dog may then be represented by the formula 

i ^ c T pm - m - x 2 = 42. 
3 1 4 3 

In each jaw there is one large specially modified tooth 
called the carnassial, the teeth in front of this are more or 
less pointed and compressed, while those behind it are more or 
less flattened and tuberculated. 

Teeth of the upper jaw. 

The first and second incisors are small teeth with long 
conical roots and somewhat chisel-shaped crowns. Surround- 
ing the base of the crown there is a rather prominent ridge, 
terminated laterally by a pair of small cusps. This ridge, the 
cingulum, serves to protect the edge of the gums from injury 
by the hard parts of food. The third incisor is a good deal 
like the others but larger, and has the cingulum well developed 
though not terminated by lateral cusps. All the incisors 
are borne by the premaxillae, the remaining teeth by the 
maxillae. 

The canine is a large pointed tooth, slightly recurved and 
with a long tapering root. 

The premolars are four in number, and in all the cingu- 
lum is fairly well seen. The first is a very small tooth with a 
single tapering root, the second and third are larger and have 
two roots, while the fourth, the carnassial, is much the largest 
and has three roots. Each of the second, third and fourth pre- 
molars has a stout blade, the middle portion of which is drawn 
out into a prominent cone ; the posterior part of the fourth 



THE SKELETON OF THE DOG. THE TEETH. 377 

premolar forms a compressed ridge, and at the antero-internal 
edge of the tooth there is a small inner tubercle. 

The two molar teeth are of very unequal size. The first, 
which has two anterior roots and one posterior, is wider than 
it is long, its outer portion being produced into two prominent 
cusps, while its inner portion is depressed. The second molar 
is a small tooth resembling the first in its general appearance, 
but with much smaller outer cusps. 

Teeth of the lower jaw. 

The three incisors of the lower jaw have much the same 
character as the first two of the upper jaw ; while the canine 
is identical in character with that of the upper jaw. 

The four premolars gradually increase in size from the 
first to the last, but none are very large. The first premolar 
is a single-rooted tooth resembling that of the upper jaw ; the 
second, third and fourth are two-rooted, like the second and 
third of the upper jaw, which they closely resemble in other 
respects. 

The first molar forms the carnassial (fig. 84, Y), and with 
the exception of the canine, is much the largest tooth of the 
lower jaw ; it is a two-rooted tooth, with a long compressed 
bilobed blade, and a posterior tuberculated talon or heel. The 
second molar is much smaller, though likewise two-rooted, while 
the third molar is very small and has only a single root. All 
the teeth except the molars are preceded in the young animal 
by temporary milk teeth. These milk teeth, though smaller, 
are very similar to the permanent teeth by which they are 
ultimately replaced. 

II. EXDOSKELETON. 
1. THE AXIAL SKELETON. 

This includes the vertebral column, the skull, and the ribs 
and sternum. 






378 THE VERTEBRATE SKELETON. 

A. THE VERTEBRAL COLUMN. 

This consists of a series of about forty vertebrae arranged 
in succession so that their centra form a continuous rod, and 
their neural arches a continuous tube, surrounding a cavity, 
the neural canal. 

The vertebrae may be readily divided into five groups : 

1. The cervical or neck vertebrae. 

2. The thoracic or chest vertebrae which bear ribs. 

3. The lumbar vertebrae which are large and ri bless. 

4. The sacral vertebrae which are fused with one another 
and united with the pelvis. 

5. The caudal or tail vertebrae which are small. 

Except in the sacral region the vertebrae are movably 
articulated to one another, while their centra are separated 
from one another by cartilaginous intervertebral discs. 

GENERAL CHARACTERS OF A VERTEBRA. 

Take as a type the fourth lumbar vertebra. It may 
be compared to a short tube whose inner surface is smooth 
and regular, and whose outer surface is thickened and drawn 
out in a variety of ways. The basal part of the vertebra 
is the centrum or body which forms the thickened floor of 
the neural canal. Its two ends are slightly convex and 
are formed by the epiphyses, two thin plates of bone which 
are at first altogether distinct from the main part of the cen- 
trum, but fuse with it as the animal grows older ; its sides are 
drawn out into a pair of strong transverse processes, which 
project forwards, outwards, and slightly downwards. The 
neural arch forms the sides and roof of the neural canal, and 
at each end just above the centrum bears a pair of interver- 
tebral notches for the passage of the spinal nerves, the pos- 
terior notches being considerably deeper than the anterior. The 
neural arch is drawn out into a series of processes. Arising 



THE SKELETON OF THE DOG. VERTEBRAL COLUMN. 379 

from the centre of the dorsal surface is a prominent median 
neural spine or spinous process, which projects upwards 
and slightly forwards ; its anterior edge is vertical, while its 
posterior edge slopes gradually. At the two ends of the 
neural arch arise the two pairs of zygapophyses or articula- 
ting surfaces, which interlock with those of the adjacent 
vertebrae. The anterior or prezygapophyses look inwards, 
and are large and concave ; they are borne upon a pair of 
large blunt outgrowths of the neural arch, the metapophyses. 
The posterior or ppstzygapophyses are slightly convex and 
look outwards and downwards ; they are borne upon back- 
warclly projecting outgrowths of the neural arch. Lastly 
there are a pair of minute projections arising from the 
posterior end of the neural arch, below the postzygapophyses. 
These are the anapophyses. In young individuals the de- 
velopment of all the processes of the various vertebrae is less 
marked, and the epiphyses are obviously distinct. 




FlG. 69. A. ATLAS AND B, AXIS VERTEBRA OF A DOG (Cams 

familiaris) (after VON ZITTEL). 



1. transverse process of atlas. 

2. vertebrarterial canal. 

3. foramen for exit of spinal 

nerve. 

4. neural spine. 

5. odontoid process. 



6. anterior articulating surface 

of centrum. 

7. centrum. 

8. transverse process of axis. 

9. postzygapophysis. 



380 THE VERTEBRATE SKELETON. 

THE CERVICAL VERTEBRAE. 

These are seven in number, as in almost all mammals. 
They are characterised by the fact that they have small ribs 
fused with them, forming transverse processes perforated by 
canals through which the vertebral arteries run. 

The first, or atlas vertebra (fig. 69, A), differs much from 
all the others ; it is drawn out into a pair of wide wing-like 
transverse processes (fig. 69, A, 1), and forms a ring surround- 
ing a large cavity. This cavity is during life divided into 
two parts by a transverse ligament ; the upper cavity is the 
true neural canal, while the lower lodges the odontoid pro- 
cess of the second vertebra, which is the detached centrum 
of the atlas. The neural arch is broad and regular ; it has 
no spinous process, and is perforated in front by a pair of 
foramina for the passage of the first spinal nerves. The mid- 
ventral portion of the atlas is rather thick, and bears a minute 
backwardly-projecting hypapophysis. The bases of the broad 
transverse processes are perforated by the vertebrarterial 
canals (fig. 69, A, 2). The atlas bears at each end a pair of 
large articulating surfaces; those at the anterior end articulate 
with the condyles of the skull, and are very deeply concave ; 
those at the posterior end for articulation with the axis, are 
nearly as large, but are flattened. The atlas ossifies from 
three centres, one forming the mid-ventral portion, the others 
the two halves of the remainder. 

The second, or axis vertebra (fig. 69, B), also differs much 
from the other cervicals. The long and broad centrum has 
a very flat dorsal surface, and is produced in front into 
the conical odontoid process (fig. 69, B, 5), and bears a 
pair of very large convex outwardly-directed surfaces for arti- 
culation with the atlas. At its posterior end it is drawn 
out into a pair of small backwardly-directed spines, the 
transverse processes ; these are perforated at their bases by 
the vertebrarterial canals. The neural arch is deeply notched 
in front and behind for the passage of the spinal nerves, and 



THE SKELETON OF THE DOG. VERTEBRAE. 381 

is drawn out above into a very long compressed neural spine 
(fig. 69, B, 4), which projects a long way forwards, and behind 
becomes bifid and thickened, bearing a pair of flat downwardly 
directed postzygapophyses. In the young animal the odontoid 
process is readily seen to ossify from a centre anterior to that 
forming the anterior epiphysis of the axis. 

The remaining five cervical vertebrae, the third to the 
seventh inclusive, have rather flattened wide centra, obliquely 
truncated at either end. The neural spine progressively increases 
in size as the vertebrae are followed back. The transverse 
processes vary considerably ; those of the third are divided 
into a thicker backwardly-, and a more slender forwardlv- 
projecting portion ; those of the fourth and fifth mainly extend 
downwards, and that of the sixth is divided into a horizontal 
portion and a downwardly-projecting inferior lamella. All 
the cervical vertebrae except the seventh have the bases of the 
transverse processes perforated by the vertebrarterial canals. 
The prezygapophyses in each case look upwards and slightly 
inwards, while the postzygapophyses look downwards and 
slightly outwards. 

THE THORACIC VERTEBRAE. 

The thoracic vertebrae are twelve or thirteen in number, 
and all bear movably articulated ribs. As a group they are 
characterised by their comparative shortness, and in the case 
of the first eight or nine by the great length of the back- 
wardly-sloping neural spine. The posterior thoracic vertebrae 
approach in character the succeeding lumbar vertebrae. 

As type of the anterior thoracic vertebrae, take any one 
between the second and sixth inclusive. The centrum is short, 
and has its terminations vertically truncated. At the top of 
the centrum, at both anterior and posterior ends on each side, 
is a demi-facet (fig. 70. A, 4), which, together with that on the 
adjacent vertebra, forms an articulating surface for the capitu- 
lum of the rib. The neural arch is small and deeply notched 



382 



THE VERTEBRATE SKELETON. 



behind for the passage of the spinal nerve. It is drawn out 
above into a very long neural spine (fig. 70, A, 1), whose base 
extends back over the succeeding vertebra and bears the down- 
wardly-directed postzygapophyses (fig. 70, A, 6). The summit 
of the neural arch is deeply notched in front, and on each side 
of the notch are the prezygapophyses, which look almost ver- 
tically upwards. The transverse processes are short and blunt, 
and are flattened below (fig. 70, A, 3) for the articulation of 
the tubercula of the ribs. 



B 




FlG. 70. A, SECOND THORACIC, AND B, SECOND LUMBAR VEETEBBA OF A 

DOG (Canis familiar is) SEEN FROM THE BIGHT SIDE (after VON ZITTEL). 



1. neural spine. 

2. centrum. 

3. transverse process bearing in 

A the facet for articulation 
with the tuberciilum of the 
rib. 



4. facet for articulation with the 

capitulum of the rib. 

5. metapophysis. 

6. postzygapophynis. 



The posterior three or four thoracic vertebrae differ much 
from the others. The centra are longer, the neural spines short 
and not directed backwards, the articular facets for the heads 
of the ribs are confined to the anterior end of the centrum of 
each vertebra, not overlapping on to the preceding vertebra. 
The transverse processes are small and irregular, and meta- 
pophyses and anapophyses are developed. The prezygapophysrs 



THE SKELETON OF THE DOG. THE VERTEBRAE. 383 

also look more inwards, and the postzygapophyses more out- 
wards than in the more typical thoracic vertebrae. 

THE LUMBAR VERTEBRAE. 

The lumbar vertebrae are seven in number, and their 
general characteristics have been already described. As a 
group they are characterised by their large size, and the great 
development of the transverse processes, metapophyses and 
neural spines. 

THE SACRAL VERTEBRAE. 

Three vertebrae are commonly found fused together, forming 
the sacrum ; the divisions between the three being indicated 
by the foramina for the exit of the spinal nerves. 

Of these three vertebrae, the first is much the largest, 
and is firmly united to the ilium on each side by a structure 
formed by the transverse processes and expanded ribs. In the 
adult this structure forms one continuous mass, but in the 
young animal a ventral portion formed by the rib is clearly 
distinguishable from a dorsal portion formed by the transverse 
process. All three have low neural spines. The anterior 
sacral vertebra bears a large pair of prezygapophyses, while 
the posterior one bears a small pair of postzygapophyses. 

THE CAUDAL VERTEBRAE. 

The caudal vertebrae are about nineteen in number. 
The earlier ones have well-developed neural arches, transverse 
processes, and zygapophyses, but as the vertebrae are followed 
back they frradually lose all their processes, and the neural arch 
as well, becoming at about the thirteenth from the end reduced 
to simple cylindrical centra. 

B. THE SKULL. 

The skull consists of the following three parts : (a) the 
< ranium. with which are included the skeletal supports of the 
various special sense organs, and the bones of the face and 
upper jaw ; (6) the lower jaw or mandible, which is movably 
articulated to the cranium, and (c) the hyoid. 



384 THE VERTEBRATE SKELETON. 

(a) THE CRANIUM. 

The cranium is a compact bony box, forming the anterior 
expanded portion of the axial skeleton. It has a longitu- 
dinal axis, the craniofacial axis around which the various 
parts are arranged, and this axis is a direct continuation of 
that of the vertebral column. Similarly the cavity of the 
cranium is a direct continuation of the spinal canal. The 
posterior part of the craniofacial axis, which has relations 
only with the cranium, is called the basicranial axis. 

In the dog as in the other types previously described, the 
skull in its earliest stages is cartilaginous, containing no bone. 
In the adult, however, the cartilage is to a great extent 
replaced by bone, and in addition to this cartilage bone, 
membrane bone is largely developed, and intimately united 
with the cartilage bone to form one complete whole. 

In the description of the dog's skeleton, as in those of the 
previous types, the names of the membrane bones are printed 
in italics, while those of the cartilage bones are printed in 
thick type. 

Most of the numerous foramina perforating the skull 
walls will be described after the bones have been dealt with. 

For purposes of description the cranium may be further 
subdivided into : 

1 . The cranium proper or brain case. 

2. The sense capsules. 

3. The upper jaw. 

1. THE CRANIUM PROPER OR BRAIN CASE. 

Taking the membrane and cartilage bones together, they 
are seen to be more or less arranged in three segments, which 
however must not be regarded as homologous with the seg- 
ments forming the vertebral column. 

The occipital segment is the most posterior of the three, 
and consists of four cartilage bones, which in the adult are 
commonly completely fused together. They surround the great 



THE SKELETON OF THE DOG. THE SKULL. 385 



vj Ui^'xc^y v.-.'^r^'-.vix N3VS9 
?Tii V \'<-^\ 7 -V VT> 5-S,-Xx^D 1 ^\-?\'-' 

I f^aSM^tM^7/SS^^ 

r. *^ \-^-^ r. '^//-i*^/-\ r\\ ^N ^ I / i \'f\ Wl On CB/.B 



12 o Wv; .8fooS oVv"^ 




FIG. 71, DIAGRAM OF THE RELATIONS OF THE PRINCIPAL BONES IN THE 
MAMMALIAN SKULL (modified after FLOWER). 

Cartilage is dotted. Cartilage bones are marked by dots and dashes, 
membrane bones are left white. 



1. basi-occipital. 

2. exoccipital. 

3. supra-occipital. 

4. basisphenoid. 

5. alisphenoid. 

6. parietal. 

7. presphenoid. 

8. orbitosphenoid. 

9. frontal. 

10. periotic, immediately below 

which is the tympanic. 

11. lachrymal. 

12. ethmo-turbinal. 

13. maxillo-turbinal. 

14. nasal. 



15. mesethmoid. 

16. vomer. 

17. pterygoid. 

18. palatine. 

19. maxilla. 

20. premaxilla. 

21. sqaamosal. 

22. mandible. 

23. tympano-hyal. 

24. stylo-hyal. 

25. epi-hyal. 

26. basi-hyal. Between this and 
the epi-hyal is the cerato-hyal. 

27. thyro-hyal. 

28. jugal. 

Nerve exits are indicated by Eoman numerals. 



EL 



386 THE VERTEBRATE SKELETON. 

foramen magnum (fig. 75, 2) through which the brain and 
spinal cord communicate. Forming the lower margin of the 
foramen magnum is a large flat unpaired bone, the basi- 
occipital (tig. 75, 5). Above this on each side are the ex- 
occipitals, whose sides are drawn out into a pair of down- 
wardly-directed paroccipital processes, which are applied 
to the tympanic bullae 1 . The inner side of each exoccipital is 
converted into the large rounded occipital condyle (fig. 72, 
13) by which the skull articulates with the atlas vertebra. The 
dorsal boundary of the foramen magnum is formed by a large 
unpaired flat bone, the supra-occipital (figs. 72' and 75, 1), 
which is continuous with a small bone, the interparietal, pro- 
longed forwards between the parietal bones of the next segment. 

In old animals the interparietal forms the hind part of a 
prominent ridge running along the mid-dorsal surface of the 
skull and called the sagittal crest, while the junction line of 
the occipital and parietal segments forms a prominent occi- 
pital crest. 

The plane in which the bones of the occipital segment lie 
is called the occipital plane ; the angle that it makes with the 
basicranial axis varies much in different mammals. 

The parietal segment consists of both cartilage and 
membrane bones. It is formed of five bones, which are in 
contact with those of the occipital segment on the dorsal and 
ventral surfaces, while laterally they are separated by the inter- 
position of the auditory bones, and to some extent of the squa- 
mosal. The basisphenoid (fig. 75, 6), an unpaired bo in- 
forming the ventral member of this segment, is the direct 
continuation of the basi-occipital. It tapers anteriorly, but is 
rather deep vertically, its upper or dorsal surface bearing a 
depression, the sella turcica, which lodges the pituitary body 
of the brain. From the sides of the basisphenoid arise the 
alisphenoids (fig. 75, 11) a pair of bones of irregular shape 
generally described as wing-like ; each gives off from its lower 
i See p. 392. 



THE SKELETON OF THE DOG. THE SKULL. 387 



10 




-33 



32 



27 



FIG. 72. VERTICAL LONGITUDINAL SECTION TAKEN A LITTLE TO THE LEFT 

OF THE MIDDLE LFXE THROUGH THE SKULL OF A DOG (CaniS faitli- 

liaris) x f . (Camb. Mus.) 



1. supra-occipital. 

2. iuterparietal. 

3. parietal. 

4. frontal. 

5. cribriform plate. 

6. nasal. 

7. mesethmoid. 

8. maxilla. 

9. vomer. 

10. ethmo-turbinal. 

11. maxillo-turbinal. 

12. premaxilla. 

13. occipital condyle. 

14. basi-occipital. 

15. tympanic bulla. 

16. basisphenoid. 

17. pterygoid. 



18. palatine. 

19. alisphenoid. 

20. internal auditory meatus. 

21. tentorium. 

22. foramen lacerum posterins. 

23. floccular fossa. 

24. coronoid process. 

25. condyle. 

26. angle. 

27. mandibular symphysis. 

28. inferior dental foramen. 

29. stylo-hyal. 

30. epi-hyal. 

31. cerato-hyal. 

32. basi-hyal. 

33. thyro-hyal. 

XII. condylar foramen. 



252 



388 THE VERTEBRATE SKELETON. 

surface a pterygoid plate, which is united in front with the 
palatine, and below with the pterygoid. The alisphenoids are 
united above with a pair of large nearly square bones, the 
parietals (fig. 73, 2), which meet one another in the mid-dorsal 
line. The line of junction is frequently drawn out into a strong 
ridge, which forms the anterior part of the sagittal crest. 

The frontal segment, which surrounds the anterior part 
of the brain, is closely connected along almost its whole 
posterior border with the parietal segment. 

Its base is formed by the presphenoid (fig. 75, 12), a 
very deep unpaired bone, narrow and compressed ventrally, 
and with an irregular dorsal surface. The presphenoid is 
continuous with a second pair of wing-like bones, the orbito- 
sphenoids. Each orbitosphenoid meets the alisphenoid 
behind, but the relations of the parts in this region are 
somewhat obscured by a number of large foramina piercing 
the bones, and also by an irregular vacuity, the foramen 
lacerum anterius or sphenoidal fissure, which lies between 
the orbitosphenoid and alisphenoid, separating the lateral parts 
of the parietal and frontal segments, in the same way as the 
space occupied by the auditory bones separates the lateral 
parts of the occipital and parietal segments. The orbito- 
sphenoids pass obliquely forwards and upwards, and are united 
above with a second pair of large membrane bones, the frontals 
(fig. 73, 3). The outer side of each frontal is drawn out into 
a rather prominent rounded postorbital process (fig. 73, 10), 
from which a ridge converges backwards to meet the sagittal 
crest. The anterior part of the frontal is produced to form 
the long nasal process, which is wedged in between the nasal 
and maxilla. 

The cranial cavity is continuous in front with the nasal or 
olfactory cavities, but the passage is partially closed by a 
screen of bone, the cribriform plate (fig. 72, o), which is 
placed obliquely across the anterior end of the cranial cavity, 
and is perforated by a number of holes through which the 



THE SKELETON OF THE DOG. THE SKULL. 



389 




13 



12 



FIG. 73. DOKSAL VIEW OF THE CKAXIUM OF A DOG (Cants fami- 
liaris) x . 



1. supra-occipital. 

2. parietal.^, 

3. frontal^. 

4. nasal. ^ 

5. maxilla (facial portion}^ 

6. premaxilla. 

7. squamosal. 

8. jugal. 



10. postorbital process of frontal. 

11. infra-orbital foramen^- 

12. anterior palatine foramen. ^ 

13. "lachrymal foramen. / 
i 1. first incisor. 

c. canine. 

pm 4. fourth premolar. 



390 THE VERTEBEATE SKELETON. 

olfactory nerves pass. The plane of the cribriform plate is 
called the ethmoidal plane, and as was the case also with 
the occipital plane, the angle that it makes with the basi- 
cranial axis varies much in different mammals, and is of 
importance. The olfactory fossa in which lie the olfactory 
lobes of the brain, is partially separated from the cerebral 
fossa, or cavity occupied by the cerebral hemispheres, by 
ridges on the orbitosphenoids and frontals. The presphenoid 
is connected in front with a vertical plate formed partly of bone, 
partly of unossified cartilage; this plate, the mesethmoid 
(fig. 72, 7), separates the two olfactory cavities which lodge 
the olfactory organs. Its anterior end always remains un- 
ossified, and forms the septal cartilage of the nose. 

The brain case may then, to use the words of Sir W. H. 
Flower, be described as a tube dilated in the middle and com- 
posed of three bony rings or segments, with an aperture at each 
end, and a fissure or space at the sides between each of them. 

2. THE SENSE CAPSULES. 

Each of the three special sense organs, of hearing, of sight, 
and of smell, is in the embryo provided with a cartilaginous 
or membranous protecting capsule ; and two of these, the 
auditory and olfactory capsules, become afterwards more or 
less ossified, and intimately related to the cranium proper. 

(1) Bones in relation to the Auditory capsules. 

These bones lie on each side wedged into the vacuity be- 
tween the lateral parts of the occipital and parietal segments ; 
they are three in number, the periotic, the tympanic and the 
squamosal. 

The periotic is the most important of them, as it replaces 
the cartilaginous auditory capsule of the embryo, and encloses 
the essential organ of hearing. It commences to ossify 
from three centres corresponding to the pro-otic, epi-otic and 
opisthotic of lower skulls, such as those of the Turtle and 
Crocodile. 



THE SKELETON OF THE DOG. THE SKULL. 



391 



These ossifications however very early combine to form a 
single bone, the periotic, which nevertheless consists of two 




FIG. 74. 



DIAGRAM OF THE MAMMALIAN TYMPANIC CAVITY AND ASSOCIATED 
PAKTS (modified from LLOYD MORGAN). 



1. external auditory meatus. 

2. tympanic membrane. 

3. malleus. 

4. incas. 

5. lenticular. 

6. stapes. 



7. fenestra ovalis. 

8. fenestra rotunda. 

9. Eustachian tube. 

10. cavity occupied by the cochlea. 

11. cavity occupied by the mem- 

branous labyrinth. 



portions, the petrous and the mastoid, differing considerably 
from one another. 

The petrous portion lies dorsally and anteriorly, and is 
much the more important of the two, as it encloses the 
essential part of the auditory organ: It forms an irregular 
mass of hard dense bone, projecting into the cranial cavity, 
and does not appear on the external surface at all. The 
mastoid portion lies ventrally and posteriorly, is smaller, 
and formed of less dense bone than is the petrous portion, 
from which it differs also in the fact that it appears on the 
surface of the skull, just external to the exoccipital. The 
petrous portion bears a ridge, which together with a ridge 



392 THE VERTEBRATE SKELETON. 

on the supra-occipital, and the tentorium (fig. 72, 21), a 
transverse fold of the dura mater 1 , separates the large cerebral 
fossa from the cerebellar fossa, which is much smaller than 
the cerebral fossa and lies behind and partly beneath it. The 
plane of the tentorium is called the tentorial plane, and the 
angles that it makes with the basicranial axis and with the 
occipital and ethmoidal planes vary much in different mammals. 

The periotic has its inner surface marked by important 
depressions, while both inner and outer surfaces are pierced 
by foramina. At about the middle of its inner surface are 
seen two deep pits, one lying immediately above the other. 
Of these the more ventral is a foramen, the internal audi- 
tory meatus (fig. 72, 20), through which the Vllth (facial) 
and Vlllth (auditory) nerves leave the cranial cavity, the 
facial nerve passing through the bone and afterwards leaving 
the skull by the stylomastoid foramen (fig. 75, VII), while 
the auditory passes to the inner ear. The more dorsal of the 
two pits is not a foramen but the floccular fossa (fig. 72, 23) 
which lodges the floccular lobe of the cerebellum. In some 
skulls another wide and shallow but fairly prominent depres- 
sion is seen dorsal to and slightly behind the floccular fossa, 
this also lodges part of the cerebellum. Behind the internal 
auditory meatus, between the periotic and exoccipital is seen 
the internal opening of the foramen lacerum posterius 
(fig. 72, 22). The shape of this opening varies. The ventro- 
anterior border of the periotic is marked by a deep notch, the 
sides of which sometimes unite, converting it into a foramen. 

On the outer side of the periotic, and clearly seen only 
after the removal of the tympanic, are two holes, the fenestra 
ovalis and the fenestra rotunda. 

The tympanic (figs. 72, 15 and 75, 4) is a greatly expanded 
boat-shaped bone, which forms the auditory bulla and lies 
immediately ventral to the periotic ; it is separated from the 

1 The dura mater is a membrane which lines the cranial cavity and 
is formed of tough connective tissue. 



THE SKELETON OF THE DOG. THE SKULL. 393 

periotic by the tympanic cavity into which the fenestra 
rotunda and the fenestra ovalis open. 

There are several other openings into the tympanic cavity. 

(a) On the external surface is a large oval opening, the 
external auditory meatus bounded by a thickened rim. 

(b) Into the outer and anterior part of the cavity the 
outer end of the Eustachian tube opens ; while the inner 
end passes through a foramen (fig. 75, 22) just external to the 
foramen lacerum medium, on its way to open into the pharynx. 

(c) The internal carotid artery also enters the tympanic 
cavity by a canal which commences in the foramen lacerum 
posterius, and passes forwards to open on the inner side of the 
bulla. The artery then passes forwards, and barely appearing 
on the ventral surface of the cranium, enters the brain cavity 
through the foramen lacerum medium (tig. 75, 9). 

Immediately behind the tympanic, between it and the 
mastoid process of the periotic and the paroccipital process of 
the exoccipital is the stylomastoid foramen (fig. 75, VIII). 

Within the tympanic cavity are four small bones, the 
auditory ossicles (cp. fig. 74), called respectively the mal- 
leus, incus, lenticular and stapes ; these together form a 
chain extending from the fenestra ovalis to the tympanic 
membrane. 

The malleus has a somewhat rounded head (fig. 100, B, 1) 
which articulates with the incus, while the other end of the 
bone is drawn out into a long process, the manubrium, 
which lies in relation to the tympanic membrane. The head 
is also more or less connected by a thin plate of bone, the 
lamella, to another outgrowth, the processus longus. The 
incus (fig. 100, B, 3) is somewhat anvil-shaped, and is drawn 
out into a process which is connected with the lenticular, a 
nodule of bone interposed between the incus and the stapes, 
with which it early becomes united. The stapes (fig. 100, B, 2) 
is stirrup-shaped, consisting of a basal portion from which 
arise two crura, which meet and enclose a space, the canal. 



394 THE VERTEBRATE SKELETON. 

The squamosal (fig. 73, 7) is a large bone occupying much 
of the side wall of the cranial cavity, and articulating above 
with the parietal, and behind with the supra-occipital, while 
in front it overlaps the frontal and alisphenoid. But though it 
occupies so large a space on the outer wall, it forms very 
little of the internal wall of the skull, but is really like a bony 
plate attached to the outer surface of the cranial wall. The 
squamosal is drawn out into a strong forwardly-directed zygo- 
matic process which meets the jugal or malar. The ventral 
side of the zygomatic process is hollowed out, forming the 
glenoid fossa (fig. 75, 8), a smooth laterally elongated surface 
with which the lower jaw articulates, while the hinder edge of 
the glenoid fossa is drawn out into a rounded postglenoid 
process (fig. 75, 23). The articulation is such as to allow 
but little lateral play of the lower jaw. 

(2) Bones in relation to the Optic capsules. 

The only bone developed in relation to the optic capsule 
on each side is the lachrymal. This is a small membrane 
bone lying between the frontal and palatine behind, and the 
maxilla and jugal in front. It is perforated by a prominent 
lachrymal foramen (fig. 73, 13) which opens within the 
orbit. 

(3) Bones in relation to the Olfactory capsules. 

In connection with the olfactory capsules, five pairs of 
bones are developed, two pairs being membrane bones, and 
three pairs cartilage bones. 

Of membrane bones, the nasals (fig. 73, 4) are a pair of 
long narrow bones, lying closely side by side, and forming 
the main part of the roof of the olfactory chamber. Their 
posterior ends overlap the froritals, and the outer margin of 
each is in contact with the nasal process of the frontal, and 
with the maxilla and premaxilla. 

Lying immediately ventral to the nasals, and on each 
side of the perpendicular rnesethmoid, are the ethmoid or 



THE SKELETON OF THE DOG. THE SKULL. 395 

turbinal bones, which have a curious character, being formed 
of a number of delicate plates intimately folded on one 
another. The posterior pair of these bones, the ethmo- 
turbinals (fig. 72, 10), are the larger, and form a mass of 
intricately folded lamellae attached behind to the cribriform 
plate, and passing laterally into two thin plates of bone, 
which abut on the maxillae. The uppermost lamella of each 
ethmo-turbinal is larger than the others and more distinct. 
It is sometimes distinguished as the naso -turbinal, and forms 
an imperfect lower boundary to a canal, which is bounded 
above by the nasals. In front of and somewhat below the 
ethmo-turbinals, lie another pair of bones of similar character, 
the maxillo-turbinals (fig. 72, 11). 

The last bone to be mentioned in connection with the 
olfactory capsules is a membrane bone, the vomer (fig. 72, 9). 
This is a slender vertically-placed bone, whose anterior part lies 
l>etween the maxillo-turbinals, while behind it extends beyond 
the mesethmoid, so as to underlie the anterior part of the pre- 
sphenoid. The anterior part of the vomer forms a kind of 
trough, while further back in the region of the ethtno-turbinals 
it sends out a pair of strong lateral plates, each of which, 
passing below the ethmo-turbinal, joins the side wall of the 
nasal cavity, and forms a partition dividing the nasal 
cavity into a lower narial passage and an upper olfactory 
chamber. 

THE JAWS. 

In the embryo both upper and lower jaws are formed of 
cartilaginous bars, but in the adult not only has the cartilage 
entirely disappeared, but even cartilage bone is absent, the 
jaws being formed of membrane bone. 

3. THE UPPER JAW. 

The bones of the upper jaw are closely connected with 
those of the cranium proper and olfactory capsules. The most 



396 



THE VERTEBRATE SKELETON. 

-'' .-2 

fek'' 31 

9 

7 
10 



14 




22 



pm4 



20 



12 



FIG. 75. VENTRAL VIEW OF THE CRANIUM OF A DOG (Canisfami- 
liaris) x . (Camb. Mus. ) 



1. supra-occipital. 

2. foramen magnum. 

3. occipital co'ndyle. 10. 

4. tympanic bulla. 11. 

5. basi-occipital. 12. 

6. basisphenoid. 13. 

7. external auditory meatus. 14. 

8. glenoid fossa. 15. 

9. foramen lacerum medium and 16. 



anterior opening of carotid 

canal. 

postglenoid foramen, 
alisphenoid. 
presphenoid. 
vomer. 
jugal. 
pterygoid. 
palatal process of palatine. 



THE SKELETON" OF THE DOG. THE SKULL. 397 

17. maxilla (palatal portion). V.,. foramen rotundum. 

18. posterior palatine foramina. V 3 . foramen ovale. 

19. anterior palatine foramen. VII. *tylomastoid foramen. 

20. premaxilla. IX, X, XI. foramen lacerom pos- 

21. alisphenoid canal. terius. 

22. Eustachian foramen. XII. condylar foramen. 

23. postglenoid process of squa- i 2. second incisor. 

mosal. c. canine. 

II. optic foramen. pm 1, pm i. first and fourth pre- 

III, IV, Vj, VI. foramen lacerum molars. 

anterius. m 1. first molar. 

posterior of them is the pterygoid (tig. 75, 15), a thin verti- 
cally placed plate of bone, which articulates above with the 
basisphenoid, the presphenoid, and the strong pterygoid pro- 
cess of the alisphenoid. The ventral end of the pteiygoid 
is drawn out into a small backwardly-projecting hamular 
process. In front the pterygoid articulates with the palatine, 
a much larger bone, consisting of (1) a vertical portion, which 
passes up to meet the orbitosphenoid and frontal, and sends 
inwards a plate which meets the presphenoid and vomer, form- 
ing much of the roof of the posterior part of the narial passage : 
and (2) a strong horizontal portion, the palatal process (fig. 
7">. 16), which passes inwards and meets its fellow in the 
middle line, forming the posterior part of the bridge of bone 
supporting the hard palate. The palatal process is continuous 
in front, with a large bone, the maxilla, which, like the pala- 
tine, consists of vertical and horizontal portions. The vertical, 
or facial portion (fig. 73, 5), is the largest, and constitutes 
the main part of the side of the face in front of the orbit, form- 
ing also the chief part of the outer wall of the nasal cavity. 
It is continuous in front with the premaxilla, above with the 
nasal and frontal, and behind with the lachrymal, jugal, and 
palatine. The horizontal, or palatal portion (fig. 7-3. 17). 
forms the anterior part of the bony plate supporting the hard 
palate, and meets its fellow in a long straight symphysis. The 
junction line between the palatal and facial portions is called 



398 THE VERTEBRATE SKELETON. 

the alveolar border, and along it are attached the canine, 
premolar, and molar teeth. 

The anterior part of the upper jaw on each side is formed 
by a small bone, the premaxilla, which bears the incisor teeth. 
It, like the maxilla, has a palatal portion (fig. 75, 20), which 
meets its fellow in the middle line, and an ascending portion, 
which passes backwards as the nasal process, tapering regu- 
larly and lying between the nasal and the maxilla. The two 
premaxillae form the outer and lower borders of the anterior 
nares. The last bone to be mentioned in connection with the 
upper jaw and face is ihejugal or malar (figs. 73, 8, and 75, 14), 
a strong bone which forms the anterior half of the zygomatic 
arch. It is firmly united in front to the maxilla, and behind 
meets the zygomatic process of the squamosal, being drawn 
out dorsally into a short postorbital process at the point of 
meeting. This process lies immediately below the postorbital 
process of the frontal, and if the two met, as they do in some 
mammals, they would partially shut off the orbit from a larger 
posterior cavity, the temporal fossa. In the living animal a 
ligament unites the two postorbital processes. 

(6) THE LOWER JAW OR MANDIBLE. 

This consists of two elongated symmetrical halves, the 
rami, which are united to one another at the median 
symphysis in front, while behind they diverge considerably, 
and each articulates with the glenoid surface of the corre- 
sponding squamosal. In young animals the rami are united at 
the symphysis by fibrous tissue, but in old animals they some- 
times become fused together. The upper or alveolar border 
bears the teeth, and behind them is drawn out into a high 
laterally compressed coronoid process (fig. 72, 24), which is 
hollowed on its outer surface. Immediately behind the coronoid 
process is the transversely elongated condyle (fig. 72, 25), 
which fits into the glenoid cavity in such ;i way as to allow 
free up and down movement of the jaw, with but little rolling 
motion. The posterior end of the jaw below the condyle forms 



THE SKELETON OF THE DOG. THE SKULL. 399 

a short rounded process, the angle (fig. 72, 26). Two promi- 
nent foramina are to be seen in the lower jaw. These are 
firstly the inferior dental foramen (fig. 72, 28), which lies 
on the inner surface below the coronoid process ; through it 
an artery and a branch of the fifth nerve enter to supply the 
teeth, and secondly the mental foramen, which lies on the 
outer side near the anterior end, and through which a branch 
of the same nerve emerges. 

(c) THE HYOID. 

The Hyoid of the dog consists of a transverse median 
piece, the basi-hyal 1 (fig. 72, 32), from which arise two pairs of 
cornua. The anterior cornu is much the longer of the two. 
and consists principally of three short separate ossifications, 
placed end to end and called respectively the cerato-hyal 1 , 
epi-hyal, and stylo-hyal. All of them are short rods of bone, 
contracted in the middle, and expanded at the ends, where they 
are tipped with cartilage. The cerato-hyal (fig. 72, 31) lies next 
to the basi hyal. The stylo-hyal is terminated by a much smaller 
bone, the tympano-hyal, which lies in a canal between the 
tympanic and periotic, and is ankylosed to the periotic just 
to the anterior and inner side of the stylomastoid foramen. 

The posterior cornu of the hyoid is much smaller than 
the anterior ; it consists of a short bone, the thyro-hyal (fig. 
72, 33), which connects the basi-hyal with the thyroid cartilage 
of the larynx. 

FORAMINA OF THE SKULL. 

The foramina, or apertures perforating the walls of the 
skull, are very numerous, and may either be due to holes 
actually penetrating the bone, or may be small vacuities 
between the margins of two elsewhere contiguous bones. 

They may be divided into two groups, the first including 

I. The holes through which the twelve cranial nerves 
leave the cranial cavity. 

1 These are not strictly homologous with the basi-hyal and cerato-hyal 
of the Dogfish. 



400 THE VERTEBRATE SKELETON. 

a. The most anterior of these nerves, the olfactory, leaves 
the skull by a number of small holes piercing the cribriform 
plate (tig. 72, 5). 

b. The second, or optic, passes out by a large hole, the 
optic foramen (fig. 75, II) piercing the orbitosphenoid. The 
optic foramen is the most anterior of the three prominent 
holes seen within and immediately behind the orbit. 

c. The third, fourth, and sixth nerves, i.e. those supplying 
the eye muscles, and with them the first or ophthalmic branch 
of the large fifth or trigeminal nerve, pass out by a large hole, 
the foramen lacerum anterius (fig. 75, III, IV, V 1} .VI), 
which, as has been already mentioned, lies between the 
orbitosphenoid and alisphenoid. 

d. Immediately behind the foramen lacerum anterius, the 
alisphenoid is perforated by a prominent round hole, the 
foramen rotundum (fig. 75, V 2 ), through which the second 
branch of the trigeminal nerve passes out. 

e. A quarter of an inch further back there is another 
prominent hole, the foramen ovale (tig. 75, V 3 ), through 
which the third branch of the trigeminal nerve leaves the 
cranium. 

f. The seventh or facial nerve, as already mentioned, 
leaves the cranial cavity and enters the auditory capsule, 
through an opening in the periotic called the internal 
auditory meatus, while it finally leaves the skull by the 
stylomastoid foramen (fig. 75, VII), which lies between 
the tympanic bulla, the paroccipital process, and the mastoid 
portion of the periotic. 

g. The eighth or auditory nerve on leaving the cranial 
cavity, passes with the facial straight into the auditory capsule 
through the internal auditory meatus (tig. 72, 20). It is 
then distributed to the organ of hearing. 

h. The ninth, tenth and eleventh nerves leave the skull 



THE SKELETON OF THE DOG. THE SKULL. 401 

through the foramen lacerum posterius (fig. 75, IX, X, 
XI), a large space lying between the auditory bones and the 
exoccipital. 

i. Finally, the twelfth nerve, the hypoglossal, passes out 
through the prominent eondylar foramen (fig. 75, XII), 
which perforates the exoccipital just behind the foramen 
lacerum posterius. 

II. OTHER OPENINGS IN THE SKULL. 

a. The anterior narial opening lies at the anterior end 
of the skull, and is bounded by the premaxillae and nasals. 
In the natural condition it is divided into two by a vertical 
partition, formed by the narial septum, the anterior un- 
ossified part of the mesethmoid. 

b. Penetrating the middle of the maxilla at the side of 
the face is the rather large infra-orbital foramen (fig. 73, 11), 
through which part of the second branch of the trigeminal 
nerve passes out from the orbit to the side of the face. 

c. Several foramina are seen perforating the anterior part 
of the orbit. The most dorsal of these, perforating the lach- 
rymal bone, is the lachrymal foramen (tig. 73, 13). Lying 
below and slightly external to this is a large foramen, through 
which part of the second branch of the trigeminal enters on 
its way to the infra-orbital foramen and so to the side of the 
face. Lastly, lying below these, and perforating the palatine, 
are two closely apposed foramina, the internal orbital 
foramina, through which part of the first or ophthalmic . 
branch of the trigeminal nerve leaves the orbit, passing into 
the nasal cavity. 

d. The anterior part of the palate between the premaxillae 
and the maxillae is perforated by a pair of long closely apposed 
apertures, the anterior palatine foramina (fig. 75, 19). 
They transmit part of the trigeminal nerve. 

e. Towards the posterior part of the palate are two pairs 
of small posterior palatine foramina (fig. 75, 18). These 

R. 26 



402 THE VERTEBRATE SKELETON. 

perforate the palatine and transmit branches of the trigeminal 
nerve and certain blood-vessels. 

f. The posterior narial opening is bounded chiefly by 
the palatines. 

g. The alisphenoid canal (fig. 75, 21) is a short canal 
penetrating the base of the alisphenoid bone, and transmitting 
the external carotid artery. It lies between the foramen 
rotundum and the foramen ovale. 

h. Between the auditory bulla and the foramen ovale are 
seen two openings. The more external of these is the opening 
of the Eustachian canal (fig. 75, 22), which communicates 
with the tympanic cavity. The more internal is the foramen 
lacerum medium (fig. 75, 9), through which the internal 
carotid enters the cranial cavity. 

i. The external auditory aperture (fig. 75, 7) is a large 
opening with rough edges at the outer side of the tympanic bulla. 

j. Between it and the glenoid surface of the squamosal is 
the postglenoid foramen (fig. 75, 10) through which a vein 
passes out. 

k. Lastly, there is the great foramen magnum (fig. 75, 2), 
between the occipital condyles. Through it the brain and 
spinal cord communicate. 

C. THE RIBS AND STERNUM. 

These, together with the thoracic vertebrae, form the 
skeletal framework of the thorax. Each rib is a curved rod, 
which at its dorsal end is movably articulated to the vertebra, 
and at its ventral end is either connected with the sternum, or 
ends freely. In the dog there are thirteen pairs of ribs, nine 
pairs of which are directly connected with the sternum, while 
the remaining four end freely and are known as floating ribs. 
Each rib is obviously divided into two parts, a dorsal or ver- 
tebral part, and a ventral or sternal part. The vertebral 
portion, which forms about two-thirds of the whole rib, is a 
flattened, regularly curved rod, completely ossified. Its dorsal 



THE SKELETON OF THE DOG. THE RIBS. 



403 



end is rounded, forming the head or capitulum, which 
articulates with a concave surface furnished partly by the cor- 
responding vertebra and partly by the vertebra next in front. 
The last three or four however articulate with one vertebra 
only. A short way behind the capitulum on the dorsal side of 
the rib is a rounded outgrowth, the tubercle or tuberculum. 
by means of which the rib articulates with the transverse 
process. The portion of the rib between the head and the 
tubercle is known as the neck. The sternal portion of the 
rib (fig. 76) is a short bar of calcified or imperfectly ossified 
cartilage, about one-third of the length of the corresponding 
bony portion. The anterior sternal ribs are somewhat more 
cartilaginous than the posterior ones. The vertebral portions 




FIG. 76. STERNUM ASH STEBXAL BIBS OF A DOG (Cams familiaris) 



1. presternum. 

2. first sternebra of mesoster- 

num. 

3. last sternebra of mesoster- 

nnm. 



4. xiphisternum. The flattened 

cartilaginous plate termi- 
nating the xiphisternum is 
not shown. 

5. first sternal rib. 

262 



404 THE VERTEBRATE SKELETON. 

increase in length from the first which is very stout, and has 
the capitulum and tuberculum very distinct, to about the 
eighth or ninth ; afterwards they gradually diminish in size. 
The first nine to eleven have the capitula and tubercula sepa- 
rate, afterwards they gradually merge together. 

THE STERNUM. 

This is an elongated cylindrical structure lying in the mid- 
ventral wall of the thorax, and is divided into eight segments 
or sternebrae. The anterior segment, the presternum 
(fig. 76, 1) or manubrium sterni is expanded in front; the 
next six segments, which, together form the mesosternum 
are elongated, somewhat contracted in the middle and ex- 
panded at the ends. The last segment or xiphisternum 
(tig. 76, 4) is long and narrow, and terminates in a flattened 
expanded plate of cartilage. The first pair of sternal ribs 
articulate with the sides of the presternum, and the remaining 
pairs between the successive sternebrae. Between the last 
sternebra and the xiphisternum two pairs articulate. De- 
velopment shows that the sternum is formed by the union 
in the middle line of two lateral portions ; this can be well 
seen in the presternum and xiphisternum of the puppy, but no 
traces of this median division remain in the adult dog. 

2. THE APPENDICULAR SKELETON. 

The appendicular skeleton consists of the bones of the 
anterior and posterior limbs, and of their respective supports, 
the pectoral and pelvic girdles. 

THE PECTORAL GIRDLE. 

The pectoral girdle lies external to the ribs, and has no 
bony attachment to the axial skeleton. In almost all 
Mammalia it is, as compared with that in Sauropsids, very 
incomplete ; and in the dog it is even more reduced than in 
the majority of Mammalia. The dorsal portion or scapula is 
well developed, but the ventral portion is almost entirely absent. 

The scapula is somewhat triangular in shape, the apex 



THE SKELETON OF THE DOG. PECTORAL GIRDLE. 405 

being directed downwards and forwards, and being expanded 
to form the shallow glenpid_cayity with which the head of 
the humerus articulates. The inner surface of the scapula is 
nearly flat, while the outer is drawn out into a very prominent 
ridge, the spine, which, arising gradually near the dorsal end, 
runs downwards, dividing the surface into two nearly equal 
parts, the prescapular and postscapular fossae, and ends 
in a short blunt process, the acromion. The anterior border 
of the scapula is somewhat curved, and is called the coracoid 
border ; it is terminated ventrally by a slight blunt swelling, 
the coracoid process, which ossifies from a different centre 
from the rest of the scapula, and is probably the sole repre- 
sentative of the coracoid. The dorsal or suprascapular 
border of the scapula is rounded, while the posterior or 
glenoid border is nearly straight. The clavicle 1 or collar 
bone, which in a large proportion of mammals is well seen, in 
the dog is very imperfectly developed ; it is short and broad, 
and is suspended in the muscles, not reaching either the 
scapula or sternum. 

THE ANTERIOR LIMB. 

The anterior limb of the dog is divisible into the usual 
three portions, the brachium or upper arm, the anti- 
brachium or fore-arm, and the manus or wrist and hand. 

The brachium or upper arm includes only a single bone, 
the humerus. 

The humerus is a stout elongated bone, articulating by 
its large proximal head (fig. 77, 1) with the glenoid cavity of 
the scapula, and at its distal end by the trochlea with the 
bones of the fore-arm. The head passes on its inner side into 
an area roughened for the attachment of muscles and called 
the lesser tuberosity (tig. 77, 2) ; while in front it is divided 
by the shallow bicipital groove from a large roughened area, 
the greater tuberosity (fig. 77, 3), which is continued as a 

1 See note to p. 25: 



406 THE VERTEBRATE SKELETON. 

slight roughened ridge, extending about one-third of the way 
down the outer side of the shaft. This ridge, which in many 
animals is much more strongly developed than it is in the dog, 
is called the deltoid ridge. The trochlea (fig. 77, 5) at the 
distal end of the bone is a pulley-like surface, elevated at 
the sides and grooved in the middle. It articulates with the 
radius and ulna of the fore-arm. On each side of it are slight 
roughened projections, the internal and external condyles 
(fig. 77, 7). In the cat and many other animals there is a 
foramen, the ent-epicondylar foramen above the internal 
condyle, but in the dog this is not developed. Passing up 
the shaft from the external condyle is a slight ridge, the supi- 
nator or ectocondylar ridge ; this is better developed in 
many mammals. Immediately above the trochlea in front 
and behind are the deep supra-trochlear fossae, which 
communicate with one another through the supra-trochlear 
foramen (fig. 77, 8). The posterior of these, the olecranon 
fossa, is much the deeper, and receives the olecranon process 
of the ulna when the arm is extended. The head and 
tuberosities of the humerus ossify from one centre, the shaft 
from a second, and the trochlea and condyles from a third. 

The fore-arm or., antibrachium contains two bones, 
the radius and ulna ; they are immovably articulated with 
one another, but not fused. The pre-axial bone, the radius 
(fig. 77, B), which lies more or less in front of the ulna, is 
external to the ulna at its proximal end, and at its distal end is 
internal to that bone. It articulates with the external portion 
of the trochlea, while the ulna articulates with the internal 
portion. It is a straight bone with its distal end slightly larger 
than its proximal end. The proximal end articulates with the 
trochlea, the distal end with the bones of the carpus. 

The post-axial bone, the ulna (fig. 77, C), has the proximal 
end much enlarged, forming the olecranon (fig. 77, 11), and 
tapers gradually to the distal end. Near its proximal end 
the ulna is marked by a deep sigmoid notch, which bears 



THE SKELETON OF THE DOG. ANTERIOR LIMB. 407 

on its inner side a concave surface (fig. 77, 12) for articulation 
with the trochlea. The pointed proximal end of the sigmoid 



4 "11 




14 



FIG. 77. BOXES OF THE LEFT CPPEB ABM AND FORE-ABM OF A DOG 

(Canis familiaris) x \. 

A, humerns (seen from the posterior side); B, radius, C, ulna, both seen 
from the anterior side. 

1. head. 

2. lesser tuberosity. 

3. greater tuberosity. 

4. shaft of the humerus. 

5. trochlea. 

6. internal condyle. 



7. external condyle. 

8. supra-trochlear foramen. 



9. proximal end of the radius. 

10. shaft of the radius. 

11. olecranon. 

12. surface for articulation with 

the trochlea. 

13. surface for articulation with 

the radius. 

14. distal end of the ulna. 



408 THE VERTEBRATE SKELETON. 

notch is called the coronoid process. Somewhat in front 
of and below the sigmoid notch is a smaller hollow (fig. 77, 13), 
with which the radius articulates. 

In the young animal the ends of both radius and ulna are 
seen to ossify from centres different from those forming the 
shafts. The epiphyses forming both ends of the radius, and the 
distal end of the ulna are large, while that at the proximal end 
of the ulna is small, and forms only the end of the olecranon. 

The Maims is divided into 

a. The carpus or wrist, formed of a group of small 
bones. 

b. The hand, which includes firstly some elongated 
bones, the metacarpals, forming what corresponds to the 
palm of the hand, and secondly the phalanges, which form the 
fingers. 

The Carpus or wrist. The carpus of the dog consists of 
seven small bones, arranged in a proximal row of three, and 
a distal row of four. It differs much from the simpler type 
met with in the newt. The largest bone of the proximal row 
is the scapho-lunar (fig. 80, 1 ), formed by the fused scaphoid 
(radiale), lunar (intermedium), and centrale ; it has a large 
convex proximal surface for articulation with the radius, and 
articulates distally with the trapezium, trapezoid, and magnum, 
and internally with the cuneiform. The cuneiform (ulnare) 
(fig. 80, 2) has a posterior rounded surface articulating with 
the ulna ; it articulates in front with the unciform, and in- 
ternally with the pisiform (fig. 80, 7), which is a compara- 
tively large sesamoid bone on the ulnar side of the carpus. 
Frequently also there is a small sesamoid bone on the radial 
side of the carpus. The trapezium (carpale 1), trapezoid 
(carpale 2), and magnum (carpale 3) (fig. 80, 5) are all small 
bones, and support respectively the first, second, and third 
metacarpals. The unciform (carpalia 4 and 5) (fig. 80, 6) 
is larger, and supports the fourth and fifth metacarpals. 



THE SKELETON OF THE DOG. PELVIC GIRDLE. 409 

The hand has five digits, each consisting of an elongated 
metacarpal, followed by phalanges, the last of which, the 
ungual phalanx, is pointed and curved, and bears the claw. 
Each of the metacarpals is seen in the young animal to have 
its distal end formed by a prominent epiphysis, and each of 
the phalanges, except those bearing the claws, has a similar 
epiphysis at its proximal end. 

The pollex (fig. 80, A, I) is far shorter than the other digits, 
and normally does not touch the ground in walking. It has 
only two phalanges, while each of the other digits has three. 
A pair of small sesamoid bones are developed on the ventral or 
flexor side of the metacarpo-phalangeal articulations of all the 
digits except the pollex. Frequently similar sesamoid bones 
occur also on the dorsal side of the phalangeal articulations. 

THE PELVIC GIRDLE. 

The pelvic girdle consists of two halves, which lie nearly 
parallel to the vertebral column. 

Each half is firmly united to its fellow in a ventral^ 
symphysis behind, and is in front expanded and united to the 
sacrum. Each half or innominate bone is seen in the young 
animal to consist of four distinct parts, the ilium or dorsal 
element, the pubis or anterior ventral element, the ischium 
or posterior ventral element, and a small fourth part, the 
acetabular or cotyloid bone, wedged in between the three 
others. These parts, though all distinct in the young animal, 
are in the adult so completely fused that their respective 
boundaries cannot be distinguished. At about the middle of 
the outer surface of the innominate bone is a very deep cavity, 
the acetabulum (fig. 78, A, 1) with which the head of the 
femur articulates ; all the bones except the pubis take part 
in its formation. 

The ilium is a rather long bone, expanded in front and 
contracted behind ; it forms about half the acetabulum. On 
its inner or sacral surface (fig. 78, 4) is a large roughened 



410 



THE VERTEBRATE SKELETON. 



patch for articulation with the sacrum ; its outer or gluteal 
surface is concave. The posterior part of the bone is flattened 
below, forming the narrow iliac surface (fig. 78, A, 5). 




10- 



FIG. 78. RIGHT INNOMINATE BONE, A, OF A FULL-GROWN TERRIER, B, OF 

A COLLIE PUPPY, x 1. 
A is seen from the ventral side, B from the inner or sacral side. 



1. acetabulum. 8. 

2. thyroid foramen. 9. 

3. supra-iliac border of ilium. 10. 

4. sacral surface. 11. 

5. iliac surface. 12. 

6. acetabular border. 13. 

7. pubic border. 14. 



ischial border. 

ischium. 

tuberosity of ischium. 

ischial symphysis. 

pubis. 

pubic symphysis. 

cotyloid or acetabular bone. 



The ischium. (fig. 78, 9) is a wide flattened bone forming 
the posterior part of the innominate bone. It meets the 
pubis ventrally, but is separated from it for the greater part 
of its length by the large obturator or thyroid foramen 
(fig. 78, 2). At its posterior end externally it bears a rather 






THE SKELETON OF THE DOG. PELVIC GIRDLE. 411 

prominent roughened ischial tuberosity (fig. 78, A, 10). 
The ischium meets its fellow in a ventral symphysis, and 
forms about one-third of the acetabulum. 




FIG. 79. FBONT VIEW OF THE LEFT LEG BONES OF A DOG (Canis 

familiaris) x \. 
A femur, B tibia, C fibula, D patella. 

1. head of femur. 5. external condyle. 

2. neck. 6. internal condyle. 

3. great trochanter. 7. fabella. 

4. shaft. 8. cnemial crest. 

The pubis (fig. 78, 12) is smaller than either the ischium 
or ilium ; it does not take part in the formation of the aceta- 
buluin, and like the ischium, meets its fellow in a ventral 
symphysis. The acetabular bone (fig. 78, B, 14) is small 



412 THE VERTEBRATE SKELETON. 

and triangular, and is wedged in between the other three. It 
forms about one-sixth of the acetabulum. 



THE POSTERIOR LIMB. 

The posterior limb, like the anterior, is divisible into three 
parts; these are the thigh, the crus or shin, and the pes. 

The thigh contains only a single bone, the femur. 

The femur is a long straight bone with a nearly smooth 
shaft and expanded ends. The proximal end bears on its 
inner side the large rounded head (fig. 79, A, 1) which 
articulates with the acetabulum. External to the head and 
divided from it by a deep pit is a large rough outgrowth, 
the great trochanter (fig. 79, 3). The deep pit is the 
trochanteric or digital fossa. On the inner side below the 
head is a smaller roughened surface, the lesser trochanter. 
The lower or distal end of the bone bears two prominent 
rounded surfaces, the condyles, which articulate with the 
tibia. They are separated from one another by the deep 
intercondylar notch, which is continued above and in front 
as a shallow groove, lodging a large sesamoid bone, the patella 
or knee-cap. At the back of the knee-joint are a pair of 
smaller sesamoids, the fabellae (fig. 79, 7). 

In the young animal there are three epiphyses to the shaft 
of the femur, one forming the head, one the great trochanter, 
and one the distal end. 

The crus or shin contains two bones, the tibia and 
fibula. The tibia is a fairly thick straight bone, expanded 
at both ends, especially at the head or proximal end. The 
proximal end is triangular in cross section, and bears two facets 
for articulation with the condyles of the femur. The anterior 
surface of the proximal, end of the tibia is marked by the 
strong cnemial crest (fig. 79, 8), which runs some way down 
the shaft. The distal end of the tibia articulates with the 
astragalus by an irregular, somewhat square surface. 



THE SKELETON OF THE DOG. POSTERIOR LIMB. 413 

The shaft of the tibia ossifies from one centre, the distal end 
from a second, and the proximal end from two more. 

The fibula (fig. 79, C) is a distinct but very slender bone, 
somewhat expanded at both ends. It lies external to the 




FIG. 80. A, BIGHT MANUS, B, EIGHT PES OF A DOG (Canis fami- 
liaris) x i (after VON ZITTEL). 



1. 



bone representing the fused 
scaphoid, lunar and cen- 
trale. 

cuneiform. 

trapezium. 

trapezoid. 

magnum. 

unciform. 

pisiform. 

first metacarpal. 



9. fifth metacarpal. 

10. astragalus. 

11. calcaneum. 

12. navicular. 

13. middle cuneiform. 

14. external cuneiform. 

15. cuboid. 

16. first metatarsal. 

The digits are numbered with 
Roman numerals. 






414 THE VERTEBRATE SKELETON. 

tibia and articulates by its proximal end with the head of the 
tibia, and by its distal end with the calcaneum. Its shaft 
and proximal end ossify from one centre, and its distal end 
from a second. 



The Pes. 

The structure of the pes corresponds closely with that of 
the manus. It is divided into : 

a. The tarsus or ankle formed of a group of small 
bones. 

b. The foot, which includes, firstly, some elongated bones, 
the metatarsals, forming what corresponds to the sole of 
the foot, and secondly the phalanges, which form the toes. 

The Tarsus. The tarsus of the dog consists of seven bones 
arranged in two rows, of two and four respectively, with a 
centrale between them. The two bones of the proximal row 
are the astragalus and calcaneum. 

The astragalus (fig. 80, 10) corresponds to the fused 
tibiale and intermedium of the typical tarsus. Its proximal 
end is much wider than its distal end, and forms a large 
rounded condyle articulating with the tibia, while its pos- 
terior end meets the navicular. It lies to the dorsal side of 
the foot. 

The calcaneum (fibulare) (fig. 80, 11), the thickest bone 
m the pes, lies somewhat behind, and to the outer side of the 
astragalus. It articulates with the astragalus and fibula, and 
is drawn out behind into a long rounded process, which forms 
the heel, and is in the young animal terminated by an epi- 
physis. Between the proximal and distal rows of tarsals is 
the navicular (centrale) (fig. 80, 12), a somewhat flattened 
and square bone articulating with the astragalus. 

The distal row of tarsals consists of four bones. The 
internal cuneiform (tarsale 1) is a smooth flattened bone 
lying to the inner side of the foot ; it articulates with the 



THE SKELETON OF THE DOG. THE PES. 415 

tirst metatarsal and with the navicular. The middle cunei- 
form (tarsale 2) (fig. 80, 13) is a still smaller bone, lying 
external to the internal cuneiform. It articulates with the 
second metatarsal and with the navicular. The external 
cuneiform (tarsale 3) (fig. 80, 14) is a larger, somewhat square 
bone lying external to the middle cuneiform. It articulates 
with the third metatarsal and with the navicular. The cuboid 
(tarsalia 4 and 5) (fig. 80, 15) is a considerably larger bone 
lying to the outer side of the foot. It articulates with the 
fourth and fifth metatarsals and with the calcaneum. 

The pes has sometimes five digits, sometimes four, the 
hallux being absent. Even when present the hallux (tig. 80, 
B, I) is commonly much reduced, and may be quite vestigial, 
and represented only by a small nodular metatarsal. 

Each of the other digits consists of a long metatarsal, 
which in the young animal has a prominent epiphysis at its 
distal end, and of three phalanges. The proximal and middle 
phalanges have epiphyses at their proximal ends, while the 
distal phalanx is without epiphyseS and is claw-shaped. 



CHAPTER XXII. 

GENERAL ACCOUNT OF THE SKELETON IN 
MAMMALIA. 

THE EXOSKELETON AND VEBTEBRAL COLUMN. 

EPIDERMAL EXOSKELETON. 

Hair, which forms the characteristic Mammalian exo- 
skeleton varies much in different animals, and in different 
parts of the same animal. A large proportion of mammals 
have the surface fairly uniformly covered with hair of one 
kind only. In some forms however there are two kinds of 
hair, a longer and stiffer kind alone appearing on the surface, 
and a shorter and softer kind forming the under fur. In 
most mammals hairs of a special character occur in certain 
regions, such as above the eyes, on the margins of the 
eyelids, and on the lips and cheeks, here forming the vibrissac 
or whiskers. 

Sometimes as in Hippopotamus, Orycteropus and the Sirenia, 
the hair, though scattered over the whole surface, is extremely 
scanty, while in the Cetacea it is limited to a few bristles 
in the neighbourhood of the mouth, or may even be absent 
altogether in the adult. In most mammals the hairs are 
shed and renewed at intervals, sometimes twice a year, before 
and after the winter. The vibrissae or large hairs which 
occur in many animals upon the upper lip, and the mane and 
tail of Equidae are probably persistent. 



THE SKELETON IN MAMMALIA. EXOSKELETON. 417 

In the hedgehogs, porcupines and Echidna certain of the 
hairs are modified and greatly enlarged, forming stiff spines. 
Similar spines occur in the young of Centetex, and in Acan- 
thomys among the Muridae. 

Several other forms of epidermal exoskeleton are met with 
in mammals, including : 

(a) Scales. These overlie the bony scutes of armadillos 
and occur covering the tail in several groups of mammals, such 
as beavers and rats. In the Manidae the body is covered by 
flat scales which overlap. 

(6) The horns of Bovine Ruminants. -. These, which must 
on no account be confused with antlers, are hollow cases of 
hardened epidermis fitting on to bony outgrowths of the frontals. 
In almost every case they are unbranched structures growing 
continuously throughout life, and are very rarely shed entire. 
In the Prongbuck A ntilocapra however they are bifurcated and 
are periodically shed. Horns are nearly always limited to a 
single pair, but the four-horned antelope Tetraceros has two 
pairs, the anteiior pair being the smaller. 

(c) The horns of Rhinoceroses. These are conical 
structures composed of a solid mass of hardened epidermal 
cells growing from a cluster of long dermal papillae. From 
each papilla there grows a fibre which resembles a thick hair, 
and cementing the whole together are cells which grow from 
the interspaces between the papillae. These fibres differ from 
true hairs in not being developed in pits in the dermis. 
Rhinoceros horns may be either one or two in number, and 
are borne on the fronto-nasal region of the skull. They vary 
much in length, the longest recorded having the enormous 
length of fifty-seven inches. 

(d) Nails, hoofs and claws. In almost all mammals 
except the Cetacea, these are found terminating the digits of 
both limbs. Nails are more or less flattened structures, 
claws are pointed and somewhat curved. In most mammals 

R. 27 



418 THE VERTEBRATE SKELETON. 

the nails tend to surround the ends of the digits much more 
than they do in man. Sometimes the nail of one digit differs 
from that of all the others; thus the second digit of the pes in 
the Hyracoidea and Lemuroidea is terminated by a long claw, 
the other digits having flat nails. In the Felidae the claws 
are retractile, the ungual phalanx with claw attached folding 
back when the animal is at rest into a sheath, above, or by 
the side of the middle phalanx. In the Sloths and Bats 
enormously developed claws occur, forming hooks by which the 
animals suspend themselves. In Notary ctes the third and 
fourth digits of the manus bear claws of great size ; simi- 
lar claws occur in Chrysochloris, being correlated in each case 
with fossorial habits. The nail at its maximum development 
entirely surrounds the terminal phalanx of the digit to which 
it is attached, and is then called a hoof. Hoofs are specially 
characteristic of the Ungulata. 

(e) Spurs and beaks are structures which are hardly re- 
presented among mammals, while so characteristic of birds. 
They are however both found in the Monotremata. In 
both Echidna and Ornithorhynchus the male has a peculiar 
hollow horny spur borne on a sesamoid bone articulated to 
the tibia. The jaws in Ornithorhynchus are cased in horny 
beaks similar to those of birds, and are provided with horny 
pads which act as teeth. 

(/) Horny plates of a ridged or roughened character 
occur upon the anterior portion of the palate, and of the maii- 
dibular symphysis in all three genera of recent Sirenia ; also 
upon the toothless anterior portion of the palate in Ruminants. 

(ff) The baleen of whales also belongs to the epidermal 
exoskeleton. It consists of a number of flattened horny plates 
arranged in a double series along the palate. The plates are 
somewhat triangular in form and have their bases attached 
to the palate at right angles to its long axis, while their apices 
hang downwards into the mouth cavity. The outer edge 
of each plate is hard and smooth, while the inner edge .mil 



THE SKELETON IX MAMMALIA. EXOSKELETON. 419 

apex fray out into long fibres which look like hair. At the 
inner edge of each principal plate are subsidiary smaller plates. 
The plates are formed of a number of fibres each developed 
round a dermal papilla in the same way as are the fibres 
forming the horns of Rhinoceros. Baleen and Rhinoceros 
horn likewise agree in that the fibres are bound together by 
less hardened epithelial cells, which readily wear away and 
allow the harder fibres to fray out. The greatest develop- 
ment of baleen occurs in the Northern Right whale, Balatna 
/nysticetus, in which the plates number three hundred and 
eighty or more on each side, and reach a length of ten or 
twelve feet near the middle of the series. 

DERMAL EXOSKELETOX. 

Mammals show two principal kinds of exoskeletal struc- 
tures which are entirely or partially dermal in origin, viz. the 
bony scutes of armadillos, and teeth. 

The bony scutes of armadillos are quadrate or polygonal 
in shape and are in general aggregated together, forming 
several shields protecting various regions of the body. The 
head is generally protected by a cephalic shield, the anterior 
part of the body by a scapular, and the posterior by a pelvic 
shield. The tail is also generally encased in bony rings, and 
scutes are irregularly scattered over the surface of the limbs. 
The mid-body region is protected by a varying number of 
bands of scutes united by soft skin, so as to allow of move- 
ment. Corresponding to each dermal scute is an epidermal 
plate. In Chlamyd op/torus the scutes are mainly confined to 
the posterior region where they form a strong vertically-placed 
shield which coalesces with the pelvis. The anterior part of 
the body is mainly covered by horny epidermal plates with 
very little ossification beneath. In the gigantic extinct 
Glyptodonts the body is covered with a solid carapace 
formed by the union of an immense number of plates, and 
there are no movable rings. The top of the head is defended 

272 



420 THE VERTEBRATE SKELETON. 

by a similar plate, the tail is generally encased in an unjointed 
bony tube, and there is commonly a ventral plastron. 

In Phocaena phocaenoides the occurrence of vestigial dermal 
ossicles has been described, and in Zeuglodon the back was 
probably protected by dermal plates. 

TEETH 1 . 

Teeth are well developed in the vast majority of mammalia, 
and are of the greatest morphological and systematic import- 
ance, many extinct forms being known only by their teeth. 
Mammalian teeth differ from those of lower animals in various 
well-marked respects. (1) They are attached only to the 
maxillae, premaxillae and mandible, never to the palatines, 
pterygoids or other bones. (2) They frequently have more 
than one root. (3) They are always, except in some Odon- 
toceti, placed in distinct sockets. (4) They are hardly ever 
ankylosed to the bone. (5) They are in most cases markedly 
heterodont. (6) They are commonly developed in two sets, 
the milk dentition and permanent dentition. 

It sometimes happens that teeth after being formed are 
reabsorbed without ever cutting the gum. This is the case, 
for instance, with the upper incisors of Ruminants. 

The form of mammalian teeth varies much, some are simple 
conical structures comparable to those of most reptiles, and 
these may either have persistent pulps, as in the case of the 
upper canines of the Walrus and the tusks of Elephants, or 
may be rooted as in most canine teeth. Some teeth have chisel- 
shaped edges, and this may be their original form, as in the 

1 See W. H. Flower, "Remarks on the homologies and notation of the 
teeth in Mammalia," J. Andt. and Physiol. norm, path., Vol. in., p. 262; 
R. Owen, Odontography, London, 1840 45; C. S. Tomes, Manual of 
Dental Anatomy, London, 1876. See also H. F. Osborn, "Recent re- 
searches on succession of teeth in Mammals," A HUT. Xutitral., xxvn., 
p. 493, and "Rise of Mammalia in N. America," Stud. Biol. Lai. Colitwh. 
Coll., Zool. I., no. 2. 



THE SKELETON IX MAMMALIA. THE TEETH. 



421 



human incisors, or may, as in those of Rodents, be brought 
about by the more rapid wearing away of the posterior edge, 
the anterior edge being hardened by a layer of enamel. 




m.c 



pma 



prru 



FIG. 81. SKULL OF A YOUNG INDIAN RHINOCEROS (R. unicornis), 

SHOWING THE CHANGE OF THE DENTITION X \. (Brit. MllS.) 



1. nasal. 

2. frontal. 

3. parietal. 

4. zygomatic process of squa- 

mosal. 

5. jugal. 

ml-,, milk incisor. 



me. milk canine. 

mpwij. milk premolar. 

Jj. first incisor. 

o. canine. 

pm. 2 , pm z , pm t . 2nd, 3rd and 

4th premolars. 
m,, m 9 . first and second molars. 



Then, again, the crown may, as in the majority of grinding 
teeth, be more or less flattened. The various terms used in 
describing some of the forms of the surface of grinding teeth 
are defined on page 345. 

The teeth of the Aard Varks are compound, and differ 
completely from those of all other mammals (see p. 425). 

As a rule, the higher the general organisation of an animal 



422 THE VERTEBRATE SKELETON. 

the better are its milk teeth developed, and the more do they 
form a reproduction on a small scale of the permanent set. 
This fact is well seen in the Primates, Carnivora and Ungu- 
lata. The method of notation by which the dentition of any 
mammal can be briefly expressed as a formula has been already 
described. The regular mammalian arrangement of teeth for 
each side is expressed by the formula 

01 \ o 

* Q c 7 P m ~A m ~o x ^ > total, 44. 
o 1 4- o 

MONOTEEMATA. In Echidna teeth are quite absent. In 
the young Ornithorhynchus 1 functional molar teeth of a multi- 
tubercular type resembling those of some Mesozoic mammalia 
are present, but in the adult they disappear, their office being 
discharged by horny plates. 

MARSUPIALIA 2 have a heterodont dentition, which has 
generally been regarded as almost monophyodont, the only 
tooth which has an obvious deciduous predecessor being the 
last premolar. The researches of Rose 3 and Kukenthal 4 tend 
to show that the teeth of Marsupials are developed in the 
same way as in other mammals, and are diphyodont. In 
the case of the premolars, teeth which are homologous with 
the permanent teeth of other mammals begin to develop as 
lateral outgrowths from the milk teeth, but afterwards be- 
come absorbed, so th.it the teeth which actually persist belong 
to the milk series. The last premolar, however, does as 
a rule develop and replace its milk predecessor; sometimes, 
however, as in Didelphys, it takes its place among the milk 
molars without replacing one of them. 

1 See E. B. Poulton, P. R. S., Feb. 1888, and Quart. J. Micr. ScL, 
Vol. xxix. 1889; also Oldfield Thomas, P. R. S., XLVI. (1889). 

2 W. H. Flower, Phil. Trans., vol. 156, pp. 631641, 1867 ; also 
Oldfield Thomas, Phil. Trans., pp. 443462, 1887. 

3 C. Rose, Anat. Anz. vn., p. 639. 

* W. Kukenthal, Anat. Anz. vi., p. 364. 



THE SKELETON IN MAMMALIA. THE TEETH. 423 

The types of dentition characteristic of the different groups 
of placental mammals may mostly be paralleled among 
the Marsupials. Thus among the polyprotodont forms the 
Didelphyidae or opossums, and some of the Dasyuridae, such 

- ',-cophilus and Thylacinus, have a typical carnivorous 
dentition with small incisors, large canines, and molars with 
pointed compressed crowns. The dental formula of Thylacinus, 

is i c pm ^m -, total 46. 

O 1 O T: 

In Myrmecobius five or six molar teeth occur on each side, 
and the total number of teeth reaches fifty-two or fifty-six. 
The teeth bear rows of tubercles, and resemble those of the 
Multituberculate mesozoic Mammals 1 , more than do those of 
any other living form. Calcified teeth have recently been 
described 2 in Myrmecobius earlier than the functional or milk 
set. This would relegate the milk teeth of mammals in general 
to a second series, and the permanent teeth to a third. In 

.31 ~2 4 
Notary ctes the dental formula 3 is given as i ^ c = pm ^ m - 

_ 1 O -i 

total 40. The canines are small, and the anterior molars 
have strongly developed cusps, and much resemble those of 
Ch rysochloris ( Insectivora). 

Among the diprotodont types the Phascolomyidae, or 
Wombats, have a dentition recalling that of the Rodents. All 
the teeth grow from persistent pulps, and the incisors have 
enamel only on the anterior surface as in Rodents. The dental 

formula is i ' - c - pm y m - , total 24. There are indications 

of a vestigial second pair of incisors. 

The Macropodidae, or Kangaroos, have a herbivorous 

2 /Q j\ 2 4 

dentition with the formula i - c - ^ pm ^ m . The incisors 

10 24 

are sharp and cutting, and are separated by a long diastema or 

1 See p. 348. - W. Leche, Morph. Jahrb. xx., pp. US 142 (1893). 
3 E. C. Stirling, P. Z. S. 1891, p. 327. 



424 THE VERTEBRATE SKELETON. 

gap from the molars, which have their crowns marked by ridges 
or cusps. There are indications of several vestigial incisors. 

Coenolestes, a remarkable form recently described from 
America, belongs to the diprotodont section, and is the only 
living member of the section known outside the Australian 
region 1 . An exceptional dentition is seen in the case of the 
extinct Thylacoleo, in which the functional teeth are reduced 
to two pairs ; one pair of large cutting incisors and one of 
compressed sharp-edged premolars. 

EDENTATA. Some Edentata, viz. the anteaters (Myrme- 
cophagidae) are, as far as is known, absolutely toothless at all 
stages of their existence ; being the only mammals except 
Echidna in which no tooth germs have been discovered ; 
others, viz. the Manidae, though showing foetal tooth germs, 
are quite toothless in post-foetal life ; others, viz. some of 
the armadillos, have the largest number of teeth met with in 
land mammals. The teeth are houiodont except in the Aard 
Yarks, and grow from persistent pulps. In the sloths (Brady- 
podidae) and the Megatheriidae, there are five pairs of teeth in 
the upper and four in the lower jaw. The teeth of sloths consist 
of a central axis of vasodentine, surrounded firstly by a thin coat- 
ing of hard dentine, and secondly by a thick coating of cement. 

In no living Edentate have the teeth any enamel; it has, 
however, been described as occurring in certain early Mega- 
theroid forms from S. America 2 , and an enamel organ has 
also been discovered in an embryo Dasypus*. In the Arma- 
dillos (Dasypodidae) the number of teeth varies from ~ or \ in 
Tatusia, to upwards of f -| in Priodon, which therefore may have 
upwards of a hundred teeth, the largest number met with in any 
land mammal. In Tatusia all the teeth except the last are 

1 0. Thomas, P. Z. S., 1895, p. 870. 

2 F.Ameghino.Bw^.^c. Argen.-x.ii. p. 437. According to H. Burmeister, 
Annal. Mus. Buenos Aires, in. 401 (1891), enamel does not occur, osteo- 
dentine having been mistaken for it. 

3 E. Ballowitz, Arch. Mikr. Anat. XL. p. 133. 



THE SKELETON IX MAMMALIA. THE TEETH. 425 

preceded by two-rooted milk teeth. The Aard Varks are 
cliphyodont, and milk teeth are also known in a species of 
Dasypius, but with these exceptions Edentates are, as far as is 
known, monophyodont. In Glyptodon the teeth are almost 
divided into three lobes by two deep grooves on each side. 

The Aard Varks (Orycteropodidae) are quite exceptional 
as regards their teeth, which are cylindrical in shape, and 
are made up of a number of elongated denticles fused to- 
gether. Each denticle contains a pulp cavity from which a 
number of minute tubes radiate outwards. These teeth are 
diphyodont and somewhat heterodont, eight to ten pairs occur 
in the upper jaw and eight in the lower, but they are not all in 
place at one time. The last three teeth in each jaw are not 
preceded by milk teeth 1 . 

SIRENIA. The teeth of Sirenia show several very distinct 
types, the least modified being that of the extinct Hali- 
theriidae, which have large incisors in the upper jaw, and five 
or six pairs of tuberculated grinding teeth in each jaw, the 
anterior ones being preceded by milk teeth. 

In both the living genera the dentition is monophyodont. 

2 11 

In Manatus the dentition is i pm and m . The incisors are 

i 1 1 

vestigial, and disappear before maturity. The grinding teeth 
have square enamelled crowns marked by transverse tuber- 
culated ridges. They are not all present in the jaw at the same 
time. In Halicore the upper jaw bears a pair of straight tusk- 
like incisors ; in the male these have persistent pulps and 
project out of the mouth ; in the female they soon cease to 
grow and are never cut. They are separated by a long 
diastema from the grinding teeth which have tuberculated 
crowns and are i or in number, but are not all in place at 
once. Several other pairs of slender teeth occur in the young 
animal, but are absorbed or fall out before maturity. In 
Rlujtina teeth are altogether absent. 

1 See Oldfield Thomas, P. R. S., vol. xi/m., p. 246 (1890). 



426 THE VERTEBRATE SKELETON. 

CETACBA. 

ARCHAEOCETI. Zeuglodon has the following dentition, 

31 5 

i ^ c - pm and m ^-, total 36. The incisors and canines are 

simple and conical ; the cheek teeth are compressed and have 
serrated cutting edges like those in some seals. 

In the MYSTACOCETI, or whalebone whales, calcified tooth 
germs probably belonging to the milk dentition are present 
in the embryo, but they are never functional, and are al- 
together absent in the adult. The anterior of these germs 
are simple, the posteiior ones are originally complex, but 
subsequently split up into simple teeth like those of the 
anterior part of the jaw. Hence according to Kiikenthal, 
who described these structures, the Cetacean dentition was 
originally heterodont. 

In the living ODONTOCETI the dentition is homodont and 
monophyodont. In some cases traces occur of a replacing 
dentition which never comes to maturity, and renders it pro- 
bable that the functional teeth of the Odontoceti are really 
homologous with the milk teeth of other mammals. Some of 
the dolphins afford the apparently simplest type of mammalian 
dentition known. The teeth are all simple, conical, slightly 
recurved structures, with simple tapering roots and without 
enamel. The dentition is typically piscivorous, being adapted 
for seizing active slippery animals such as fish. The prey is 
then swallowed entire without mastication. Sometimes the 
teeth are excessively numerous, reaching two hundred or more 
(fifty to sixty on each side of each jaw) in Pontoporia. This 
multiplication of teeth is regarded by Kiikenthal as due to the 
division into three parts of numbers of trilobed teeth similar to 
those of some seals. 

In the Sperm whale, Physeter, the lower jaw bears a series 
of twenty to twenty-five stout conical recurved teeth, while in 
the upper jaw the teeth are vestigial and remain imbedded in 
the gum. An extinct form, Physodon, from the Pliocene of 



THE SKELETON IN MAMMALIA. THE TEETH. 4'2T 

Europe and Patagonia is allied to the Sperm whale, but has 
teeth in both jaws. In the Grampus Orca, the teeth number 
about 14, and are very large and strong. In some forms the 
teeth are very much reduced in number; thus in Mesoplodon 
the dentition consists simply of a pair of conical teeth borne 
in the mandible. In the Narwhal Monodon the dentition is 
practically reduced to a single pair of teeth, which lie horizon- 
tally in the maxilla, and in the female normally remain perma- 
nently in the alveoli. In the male the right tooth remains 
rudimentary, while the left is developed into an enormous 
cylindrical tusk marked by a spiral groove. Occasionally both 
teeth develop into tusks, and there is reason for thinking that 
two-tusked individuals are generally or always female. In the 
extinct Squalodon the dentition is decidedly heterodont, and 
the molars have two roots. The dental formula is 

i 5- c Y pm m - , total 60. 

O I 4 t 

It is probable that the homodont condition of modern Odonto- 
ceti is not primitive, but due to retrogressive evolution. 

UXGULATA. 

Just as in the Cetacea a piscivorous dentition is most 
typically developed, so the Ungulata are, as a group, the most 
characteristic representatives of a herbivorous dentition in its 
various forms. 

UNGULATA VERA. 

ARTIODACTYLA. As regards the living forms, the Artio- 
dactyla can be readily divided into two groups, namely those 
with bunodont and those with selenodont teeth. It has, how- 
*ever, been shown that selenodont teeth always pass through 
an embryonic bunodont stage '. The bunodont type is best seen 
in Pigs and Hippopotami and such extinct forms as Hyotherium. 

.(23) 1 4 3 

In Hippopotamus the dental formula is ^ n ~ c - pm- m ~ . 

(1 o) 1 -to 

1 J. Taeker, "Fur Kenntniss der Odontogenese bei Ungulaten." Dorpat, 
1892. 



428 THE VERTEBRATE SKELETON. 

The incisors and canines of Hippopotamus are very large 
and grow continuously. The genus Sus, which affords a good 
instance of an omnivorous type of dentition, has the regular 

O -I A O 

unmodified Mammalian dental formula i ^ c y pm -m -, total 

O 1 4r O 

44. The canines, specially in the male, are large and have 
persistent pulps, and the upper canines do not have the usual 
downward direction but pass outwards and upwards. In the 
Wart Hog, Phacochaerus, they are enormously large, but a 
still more extraordinary development of teeth is found in 
Babirussa. In the male Babirussa the canines, which are with- 
out enamel, are long, curved and grow continuously. Those of 
the upper jaw never enter the mouth, but pierce the skin of 
the face and curve backwards over the forehead. The dental 

21 23 
formula of Babirussa is i ^ c -^pm ^m, total 34. 

1 2> o 

The Wart Hog has a very anomalous dentition, for as 
age advances all the teeth except the canines and last molars 
show signs of disappearing ; both pairs of persisting teeth are 
however very large. 

Various extinct Ungulata such as Anoplotherium have 
teeth which are intermediate in character between the bun- 
odont and selenodont types. Anoplotherium has the regular 
mammalian series of forty-four teeth. The crowns of all the 
teeth are equal in height, and there is no diastema an 
arrangement found in no living mammal but man. 

We come now to the selenodont Artiodactyla. 

The Tylopoda camels (Camelidae) and Llamas (Auchenii- 
dae) when young have the full number of incisors, but in the adult* 
the two upper middle ones are lost. The molars are typically 
selenodont and hypsodont 1 . In the Camel the dental formula 

11 33 
is i - c ^pm n m i5, total 34. The upper incisors, canines and 

O 1 O 

first premolars of the Camel are very small teeth, and the 

1 See p. 34o. 



THE SKELETON IX MAMMALIA. THE TEETH. 429 

first premolar is separated by a long diastema from the 
others. 

The Tragulina or Chevrotains have no upper incisors, while 
the canines are largely developed, especially in the male. 

The Ruminantia or Pecora are very uniform as regards 
their dentition. The upper incisors are always absent, for 
though their germs are developed they are reabsorbed without 
ever becoming visible, and as a rule the upper canines are 
absent too, while the lower canines are incisiform. The 
grinding teeth are typically selenodont, and in the lower jaw 
form a continuous series separated by a wide diastema from 
the canines. The dental formula is usually 

.0 01 3 3 
*gc- 1 pm^n-. 

The canines are largely developed in the male Muskdeer 
(Moschus) and in Hydropotes. 

PERISSODACTYLA. The premolars and molars have a very 
similar structure and form a continuous series of large 
square teeth with complex crowns. The crowns are always 
constructed on some modification of the bilophodont 1 plan, as 
is easily seen in the case of the forms with brachyclont teeth, 
but in animals like the Horse, in which the teeth are very 
hypsodont, this arrangement is hard to trace. All four pre- 
molars in the upper jaw are preceded by milk teeth, while in 
Artiodactyla the first has no milk predecessors. 

In the Tapiridae the grinding teeth are brachydont and 
the lower ones are typically bilophodont. The last two upper 
molars have the transverse ridges united by an outer longi- 

31 43 

tudinal ridge. The dentition is i ^ c ^ pm -m-, total 42. 

31 33 

In some of the extinct Perissodactyles such as Lophiodon 3 , 

1 See p. 345. 

- According to H. F. Osborn, Amer. Natural., xxvi. p. 763, a number of 
not very closely allied forms have been included under Lophiodon. 



430 THE VERTEBRATE SKELETON. 

the dentition is brachydont and bilophodont, the grinding 
teeth in general resembing the posterior upper molars of the 
Tapir. The same type of brachydont tooth is seen in Palaeo- 
therium but the transverse ridges are crescentic instead of 
straight, and are separated from one another by shallow 
valleys without cement. Some of the Palaeotheridae have the 
regular series of forty-four teeth. 

A complete series of forms is known showing how from the 
simple brachydont teeth of the Palaeotheridae, were derived 
the complicated hypsodont teeth of the Equidae. The increase 
in depth of the tooth was accompanied by increase in the 
depth and complexity of the enamel infoldings, and of the 
cement filling them. 

Both upper and lower grinding teeth of the Equidae are 
much complicated by enamel infoldings, but their derivation 
from the bilophodont type can still be recognised. The 
diastema in front of the premolars is longer in the living 
Equidae than in their extinct allies. In the adult horse the 

31 33 

dental formula is i ^ c ^pm-=m-^, total 40, with often a 
o 1 o o 

vestigial first upper premolar (fig. 82, pm 1). The last molar is 
not more complex than the others, and in the female the canine 
is quite vestigial. The incisors are large and adapted for cutting 
and have the enamel curiously folded in forming a deep pit. 

30 3 

The milk dentition is di -^ dc - dpm - , total 24. The last 

o U o 

milk premolar is not more complex than the premolar that 
succeeds it. The horse affords an excellent instance of a 
typically herbivorous type of dentition, the cutting incisors, 
reduced canines and series of large square flat-crowned grinding 
teeth being most characteristic. 

In Rhinoceros the grinding teeth are much like those of 
Lophiodon, having an outer longitudinal ridge from which two 
crescentic transverse ridges diverge. The upper premolars are 
as complex as the molars, and there are no canines; in some 



THE SKELETON IN MAMMALIA. THE TEETH. 431 



.1 



--5 




1.1 



FIG. 82. PALATAL ASPECT OF THE CRANIUM AND MANDIBLE or A 
DONKEY (Equus asinus) x |. (Camb. Mas.) 

1. supra-occipital. 6. glenoid surface. 

2. occipital condyle. 7. vomer. 

3. basi-occipital. t 1, 1 3. first and third incisors. 

4. vacuity representing the con- c. canine. 

fluent foramen lacerum pin 1, pm 2. first and second pre 
posterins and foramen la- molars, 

cerum medium. m 1. first molar. 

5. auditory bulla. 



432 THE VERTEBRATE SKELETON. 

species incisors also are absent. The dental formula is 
. (02) 43 

i ( o=T) c <o=X)^i w 3- 

Among the Titanotheriidae Palaeosyops 1 has very brachy- 
dont teeth whose crowns have been described as buno-selenodont, 
the inner pair of columns being bunodont, the outer, seleno- 
dont. Similar grinding teeth occur in Chalicotherium. Some 
of the Titanotheriidae have the regular mammalian series of 
forty -four teeth. 

SUBUNGULATA. 

TOXODONTIA. Nesodon has the regular dental formula : 
its grinding teeth are rooted and the upper ones resemble those 
of Rhinoceros. The second upper and third lower incisors 
form ever-growing tusks. There is a marked difference between 
the deciduous and permanent dentition. Astrapotherium like- 
wise lias large rooted cheek teeth of a rhinocerotic type, and 
each jaw bears a pair of permanently growing tusks, those 
of the lower jaw being the canines. The dental formula is 

10 23 
i -z c - pm -m^, total 28. 

O I L O 

In Toxodon, the upper incisors and molars are large and curved 
and all the teeth have persistent pulps. In Typotherium there 
are no tusks, but the upper incisors are chisel-like, recalling 
those of Rodents. 

The CONDYLAHTHKA have brachydont, generally bunodont 
teeth, with the premolars simpler than the molars. They 
generally have the regular dental formula. 

HYKACOIDEA. The dental formula of Procavia is usually 

given as i ~ c ^pm 7 m o > total 34; in young individuals how- 
ever there occur a second pair of upper incisors which early 
fall out. The upper incisors resemble those of Rodents in 
being long and curved and growing from persistent pulps. 

1 C. Earle, J. Ac. Philad., vol. ix., 1892, p. 267. 



THE SKELETON IN MAMMALIA. THE TEETH. 433 

They are however triangular iu transverse section, not rect- 
angular, having two antero-lateral faces covered with enamel 
and a posterior face without enamel. Their terminations 
are pointed, not chisel-shaped as in Rodents. The lower in- 
cisors (fig. 83, i 1) are pectinate or partially divided by vertical 
fissures, and the grinding teeth are of the rhinocerotic type. 

2 



6 




-1.1 



1.1 

FIG. 83. SKULL OF Procavia (Dendrohyrax) dorsalis x |. (Camb. Mas.) 
1. nasal. o. jugaL 

2. parietal. 6. lachrymal foramen. 

3. external auditory meatus. i 1. first incisor. 

4. paroccipital process of the 

exoccipital. 

AMBLTPODA. Two of the best known forms belonging to 
this extinct group differ much as regards dentition. For while 
Coryphodon has the regular dental formula, and the canines 
of both jaws of moderate size, in Uintatherium the dentition 
is very specialised, there are no upper incisors, and the upper 
canines form a pair of enormous tusks. The grinding teeth 
form a continuous series marked by V-shaped ridges and the 

01 33 
dental formula is i ^ c ^ p m Q m ^ total 34. 

O 1 O O 

PROBOSCIDEA. The incisors are composed entirely of den- 
tine and have the form of conical tusks projecting greatly 
R. 28 



434 THE VERTEBRATE SKELETON. 

from the mouth. In living forms they are confined to the 
upper jaw, in some species of the extinct Mastodon however 
they occur in the lower jaw also. In Dinotherium they are 
probably absent from the upper jaw, but form a pair of 
downwardly and backwardly-directed tusks growing from the 
elongated symphysis of the mandible. 

The grinding teeth in the various Proboscidea show a very 
remarkable series of modifications. In Dinotherium they are 
bilophodont or else are marked by three straight transverse 

1 2 3 

ridges. The dental formula is i ' c - pm ^m- , and the 

1 U J-i o 

teeth have the normal method of succession. In Masto- 
don as in Dinotherium the grinding teeth are marked by 
transverse ridges, but the ridges are subdivided into conical or 
mammillary cusps, and similar cusps often occur between 
the ridges. These cusps are covered with very thick enamel 
and the spaces between them are not filled up with cement. 
There are six of these grinding teeth for each side of each 
jaw but only three are in place at once. The first three are 
milk teeth as they may be succeeded vertically by others. 

In the true Elephants the number and depth of the enamel 
folds is much increased, and the spaces between the folds are 
filled up with cement. A very complete series of extinct 
forms is known with teeth intermediate in character between 
those of Mastodon and those of the Mammoth and living 
elephants. The dental formula of Elephas is 
.1.1 34 3 

Sir W. H. Flower describes ' the mode of succession of teeth 
in Elephants as follows : " As regards the mode of succession 
that of modern Elephants is as before mentioned very peculiar. 
During the complete lifetime of the animal there are but six 
molar teeth on each side of each jaw with occasionally a rudi- 
mentary one in front, completing the typical number of seven. 
1 Encyclopaedia Britannica, article Mammalia, p. 424. 



THE SKELETON IN MAMMALIA. THE TEETH. 435 

The last three represent the true molars of ordinary mammals, 
those in front appear to be milk molars which are never re- 
placed by permanent successors, but the whole series gradually 
moves forwards in the jaw, and the teeth become worn away 
and their remnants cast out in front while development of 
others proceeds behind. The individual teeth are so large 
and the processes of growth and destruction by wear take 
place so slowly, that not more than one or portions of two 
teeth are ever in place and in use on each side of each jaw 
at one time, and the whole series of changes coincides with 
the usual duration of the animal's life. On the other hand 
the Dinotherium, the opposite extreme of the Proboscidean 
series, has the whole of the molar teeth in place and use at 
one time, and the milk molars are vertically displaced by pre- 
molars in the ordinary fashion. Among Mastodons trans- 
itional forms occur in the mode of succession as well as in 
structure, many species showing a vertical displacement of 
one or more of the milk molars, and the same has been ob- 
served in one extinct species of Elephant (E. planifrons) as 
regards the posterior of these teeth." 

In the TILLODOSTIA the grinding teeth are of Ungulate 
type, while the second incisors are large and grow from per- 
sistent pulps, so as to resemble those of Rodents. 

RODEXTIA have a most characteristic and very constant 
dentition, the common dental formula being 

i j c Q pm TQ pv m 3 > total 18 or 20. 

The incisors always have chisel-like edges and persistent 
pulps, and are separated by a wide diastema from the 
premolars. Canines are always absent, and there are ge- 
nerally three grinding teeth not preceded by milk teeth ; 
their surface may be grooved, or may be bunodont. Teeth 
are most numerous in the Duplicidentata (Hares and Rabbits), 

20 33 
in which the formula is i y c -pm- m ^, total 28, and fewest 

282 



436 



THE VERTEBRATE SKELETON. 



in Hydromys and certain other forms, in which the formula is 

.10 02 

i Y c ^ pm - m -, total 1 2. The hares and rabbits are the 




777 



VI 



FIG. 84. CABNASSIAL OR SECTOBIAL TEETH or CARNIVORA (from 
FLOWER). 

Upper suctorial teeth of I. Felis, II. Canis, III. Ursus. 1. anterior, 
2. middle, 3. posterior cusp of blade, 4. inner lobe supported on distinct 
root, 5. inner lobe posterior in position and without distinct root, 
characteristic of the Ursidae. 

Lower sectorial teeth. , 1. Felis, 2. Cards, 3. Herpestex. 1. anterior, 
2. posterior lobe of blade, 3. inner tubercle, 4. heel. 



THE SKELETON IN MAMMALIA. THE TEETH. 437 

only rodents which have well developed deciduous incisors, 
though a vestigial milk incisor has been described in the 
Mouse (Jfus musculus). The last upper molar of Hydrochaerus 
is very complicated, its structure approaching that of the teeth 
of Elephants. 

CARyivoRA have the teeth rooted and markedly diphyodont 
and heterodont. The canines are greatly developed, and the 
incisors are small. 

In CARXIVORA VERA. the incisors are almost always f . The 
fourth upper premolar and first lower molar are differentiated 
as carnassial teeth (see p. 436), and retain fundamentally the 
same characters throughout the suborder. The upper car- 
nassial (fig. 84, I. II. III.) consists of a more or less compressed, 
commonly trilobed blade borne on two roots, with an inner 
tubercle borne on a third root. The lower carnassial has only 
two roots ; its crown consists of a bilobed blade with generally 
an inner cusp, and a heel or talon (fig. 84, 4) behind the blade. 

The most thoroughly carnivorous type of dentition is seen 
in the ^luroidea, and especially in the cat tribe (Felidae). In 

31 31 

the genus Felis the dental formula is i = c -= pm ^m-, total 30. 

31 21 

The incisors are very small, so as not to interfere with the 
action of the large canines, the lower carnassial is reduced to 
simply the bilobed blade (fig. 84, IV), and the cheek teeth are 
greatly subordinated to the carnassial. The extinct Machae- 
rodus has the upper canines comparable in size to those of the 
Walrus. 

The Civets and Hyaenas have a dentition allying them 
closely to the cats. The hyaena-like Proteles has, however, 
the grinding teeth greatly reduced. 

In the Cynoidea 1 the general dentition is i = c = pm - m ^ , 

ox T <5 

total 42. This differs from the regular mammalian dentition 

1 See T. H. Huxley, "The dental and cranial characters of the 
Cauidae," P. Z. S., 1880, p. 238. 



438 



THE VERTEBRATE SKELETON. 



only in the absence of the last upper molar. The upper 
carnassial tooth (fig. 84, II.) consists of a larger middle and 
smaller posterior lobe with hardly any trace of an anterior 
lobe. The lower carnassial (fig. 84, V.) is typical, consisting 
of a bilobed blade with inner cusp and posterior talon. 

The dentition of the Cynoidea is most closely linked with 
that of the Arctoidea by means of fossil forms. 

In the Arctoidea the dentition is not so typically carnivorous 




FIG. 85. MANDIBLE OF ISABELLINE BEAK (Ursus isabellinus) x 

(Camb. Mus.) 

condyle. m 1. 

coronoid process, 
first incisor. 



1. 

a. 

i 1. 
c. canine. 

pm 1, pm 2. first and second pre- 
molars. 



first molar. The dotted 
line is pointing to the pos- 
terior half of the tooth. 



This specimen has only 
three premolars, there 
should be four. 



THE SKELETON IN MAMMALIA. THE TEETH. 439 

as in the ^Eluroidea and Cynoidea. In the bears, Ursidae, 
the molars have broad flat tuberculated crowns (fig. 85). The 

.31 42 

dental formula in Ursus is i '. = c =- pm - m -^, total 42. The 

91 -t o 



upper carnassial (tig. 84, III.) differs from that of the 
roidea and Cynoidea in having no inner lobe supported on a 
third root. In the large group of Mustelidae there are gene- 
rally two molars in the lower and one in the upper jaw. The 
grinding teeth commonly have large, flattened, more or less 
tuberculated crowns, and the upper molar may be as large or 
much smaller than the carnassial. 

In the CREODOXTA there are no specially differentiated 
carnassial teeth. 



pml 




FIG. 86. LEFT MAXDIBULAR RAMUS OF THE SEA LEOPARD (Ogmorhinus 
leptonyx) WITH THE BOOTS OF THE TEETH EXPOSED x . (Camb. Mus.) 

1. condyle. pml, pm^. first and fourth pre- 

2. coronoid process. molars. 
i 3. third incisor. m. molar. 

c. canine. 

In the PIXSIPEDIA the dentition differs considerably from 
that of the Carnivora vera. The milk dentition is always 
vestigial, and the teeth are frequently absorbed before birth. 
There are four premolars and one molar, forming an uniform 
series of cheek teeth, all of which except in the Walrus have 
compressed and pointed, never flattened, crowns. There is 
no special carnassial tooth, and the incisors are always fewer 
than 'i. In Otaria the dentition is 

i -^c pm - m - , total 34 or 36. 



440 THE VERTEBRATE SKELETON. 

In the Walrus the upper canines form immense tusks. The 
other teeth are all small and one-rooted, and the molars have 
flat crowns. In the true seals the dentition is strikingly pis- 
civorous, the cheek teeth often having accessory cusps (fig. 86). 

The INSECTIVORA are diphyodont and heterodont, having 
well-developed rooted teeth. The canines are usually weak, 
the incisors pointed, and those of the two jaws often meet 
like a pair of forceps. The crowns of the molars are charac- 
teristically studded with short cusps. Some genera, such as 
Gymnura and the mole, Talpa, have the regular mammalian 
dentition. In the hedgehog, Erinaceus, the dentition is 

31 33 

* o c T P m o m o ' ttal 36. 
'2i 1 2 o 

In the genus Sorex (Shrews) the teeth differ in the following 
two marked respects from those of most other Monodelphia, 
(1) they are monophyodont, (2) the lower incisors sometimes 
become fused to the jaws. Most Insectivora have square molar 
teeth, but in Potamogale, Chrysochloris, Solenodon and the 
Centetidae the molar teeth are triangular in section. Four 
molars occur in Centetes. 

In the aberrant genus Galeopithecus the dentition is 

21 23 

i ^ c -r pm ^ m ~, total 34. The upper incisors are placed at 
o I i o 

some distance from the anterior end of the jaw, and the outer 
upper incisors and canines of both jaws have two roots, a 
very unusual character. The lower incisors are deeply grooved 
or pectinated in the same way as are the lower incisors of Pro- 
cavia. The upper incisors and canines of both jaws bear many 
cusps, and are very similar in appearance to the cheek teeth of 
some Seals. 

The dentition of the CHIROPTERA is diphyodont and hetero- 
dont, and the dental formula never exceeds 

21 33 
i s c T pm = m q , total 38. 
o 1 o o 



THE SKELETON IN MAMMALIA. THE TEETH. 441 

The milk teeth are very slender and have sharp recurved cusps : 
they are quite unlike the permanent teeth. The permanent 
teeth are of two types. In the Insectivorous forms the molar 
teeth are cusped, and resemble those of Insectivora. In the 
blood-sucking Vampire bat Desmodus, the teeth are peculiarly 
modified ; the canines and the single pair of upper incisors are 
much enlarged and exceedingly sharp, while all the other 
teeth are much reduced in size. 

In the Frugivorous bats the molar teeth have nearly always 
smooth crowns. The dental formula in the chief genus Pteropus 

.21 32 
is \ - c Y pm - m - , total 34. 
21 GO 

The PRIMATES have a diphyodont and heterodont dentition, 
generally of an omnivorous type, with cheek teeth adapted for 
grinding. The incisors are generally , and the molars, except 
in the Hapalidae, are . In the Lemurs the upper canines 
are large, and the lower incisors slender and directed almost 
horizontally forwards. The Aye Aye, Chiromys, has the follow- 
ing singular dentition : t = c ^ pm ^ m ^ , total 18. The in- 
1 U u o 

cisors much resemble those of rodents having persistent pulps, 
and enamel only on the anterior face. 

In Man and in the Anthropoid and Old World Apes 

21 23 
the dental formula is always i ^ c - pm = m = , total 32. 

a 1 a S 

In the Cebidae there is an extra premolar in each jaw 
bringing the number up to 36. In the Hapalidae, as in the 
Cebidae, there is a third premolar, but the molars are reduced 
to . Man is the only Primate that has the teeth arranged 
in a continuous series. In all the others there is a gap or 
diastema of larger or smaller size between the incisors and 
canines. In all except man also the canines are enlarged, 
especially in the males. 



442 THE VERTEBRATE SKELETON. 

The Exoskeletal structures of mammals may be summarised 
in the following table : 

I. Epidermal exoskeletal structures. 

1. Hairs (a) ordinary hair, 

(6) vibrissae and bristles, 

(c) spines of hedgehog, porcupine, Echidna, 
Centetes, Acanthomys. 

, ( of Manidae, 

2. Scales 1 

{ on tails 01 rats, beavers, &c. 

3. Horns of Rhinoceros. 

4. Horns of Bovine Ruminants. 

5. Nails, claws, hoofs. 

6. Spurs of male Ornithorhynchus and Echidna. 

7. Horny beak and teeth of Ornithorhynchus. 

8. Horny pads on jaws of Sirenians and Ruminants. 

9. Baleen of whales. 
10. Enamel of teeth. 

II. Dermal exoskeletal structures. 

1. Dentine and cement of teeth. 

2. Bony scutes of Armadillos. 

ENDOSKELETOK 

VERTEBRAL COLUMN. 

CERVICAL VERTEBRAE. 

The cervical vertebrae of all mammals have certain cha- 
racters in common. However long the neck may be, the 
number of cervical vertebrae, with very few exceptions, is 
seven. Movable ribs are generally absent, and if present 
are small and do not reach the sternum. The transverse 
processes are generally wide but not long, and are perforated 
near the base by the vertebrarterial canals, through which 
the vertebral arteries pass ; they generally bear downwardly- 
directed inferior lamellae which are sometimes as in the seventh 
human cervical seen to ossify from centres distinct from those 



THE SKELETON IN MAMMALIA. VERTEBRAL COLUMN. 443 

forming the rest of the transverse process, and are really of 
the nature of ribs. The atlas and axis always differ much 
from the other vertebrae. 

We may pass now to the special characters of the cervical 
vertebrae in the different groups. In MOXOTREMES and MAR- 
SUPIALS the number of cervical vertebrae is always seven. With 
the exception of the atlas of Echidna the cervical vertebrae 
of Monotremes are without zygapophyses. In Monotremes the 
transverse processes ossify from centres distinct from that form- 
ing the body, and remain suturally connected with the rest of 
the vertebra until the adult condition is reached. The method 
of the ossification of the atlas in Marsupials varies considerably, 
thus in some forms such as the Wombats (Phascolomys) there is 
an unossified gap in the middle of the inferior arch of the atlas, 
which may remain permanently open ; in Thyladnus this gap 
is filled up by a distinct heart-shaped piece of bone, while in 
Diddphys and Peranvl.es the atlas is ossified below in the same 
way as in other mammals. In Xotoryctes the second to sixth 
cervical vertebrae are ankylosed together. 

The cervical vertebrae of the EDENTATA have some remark- 
able peculiarities. In the three-fingered Sloth, Bradypu*, 
there are nine cervical vertebrae, all except the last of which 
have their transverse processes perforated by the vertebrar- 
terial canals. In a two-fingered sloth, Choloepus hojfmanni, 
there are only six cervical vertebrae. In the Megatheriidae, 
Anteaters (Myrmecophagidae), Pangolins (Manidae), and Aard 
Varks (Orycteropodidae), the cervical vertebrae are normal, 
but in the Armadillos (Dasypodidae), and still more in the 
Glyptodonts, several of them are commonly fused together. 
The fusion affects not only the centra, but also the neural 
arches, so that the neural canals form a continuous tube. 

In the Glyptodonts there is a complex joint at the base of 
the neck to allow the partial retraction of the head within the 
carapace. This arrangement recalls that in Tortoises. 

Asa rule the SIREXIA possess seven short cervical vertebrae, 



444 



THE VERTEBRATE SKELETON. 



not fused together and not presenting any marked peculiarities. 
In Manatus however there are only six cervical vertebrae and 
they are very variable. 

In the CETACEA there are invariably seven cervical verte- 
brae, but they are always very short and are frequently even 
before birth fused together by their centra into one continuous 
mass (see fig. 67). Sometimes the last one or two are free. In 
the Rorquals (Balaenoptera) however, the cervical vertebrae are 




FIG. 87. CERVICAL VERTEBRAE OF 
musculus) x ^. 

1. surface on the atlas for arti- 

culation with the occipital 
condyle of the skull. 

2. foramen for exit of the first 

spinal nerve. 

3. upper transverse process. 

4. lower transverse process. 



A YOUNG FIN WHALE (Balaenoptera 
(Camb. Mus.) 

In the fresh specimen these two 
transverse processes are united by 
cartilage, in adult individuals the 
whole transverse process is ossified. 

5. epiphyses of centrum. 

6. neural spine. 



quite separate and distinct (fig. 87), and in the fluviatile Odon- 
toceti, Platanista, Inia, and Pontoporia, and also in JJeluga 
and Monodon, though very short they are free. In Physeter 
the first vertebra is free while the others are fused. An 
odontoid process is not commonly present even in Cetaceans 
with free cervical vertebrae, but a very short one occurs in 
the Rorquals. The cervical vertebrae of Rorquals give off 
on each side two transverse processes (fig. 87, 3 and 4) which 



THE SKELETON IX MAMMALIA. VERTEBRAL COLUMN. 445 



enclose between them a wide space. These processes are not 
completely ossified till the animal is adult. 

In all UXGULATA the number of cervical vertebrae is seven. 
Among the Artiodactyla two forms of the odontoid process of 
the axis occurs ; in the Suina and Tragulina it is conical, in 
the Ruminantia and Tylopoda it is spout-like (fig. 88, 4). The 
atlas in the Suina and to a less extent in the Ruminantia has 

8 



--a 




5- 



Fm. 



A B 

ATLAS (B) AND AXIS (A) VERTEBRAE OF AN Ox (Bos 
taunts) x^. (Camb. Mus. ) 



anterior opening of the verte- 

brarterial canal, 
foramen for the exit of the 

second spinal nerve, 
neural spine, 
postzygapophysis. 



1. neural canal. 6. 

2. transverse process. 

3. surfaces for articulation with 7. 

the occipital condyles of 

the skull. 8. 

4. spout-like odontoid process. 9, 

5. hypapophysis. 

long flattened transverse processes, and the remaining cervical 
vertebrae are opisthocoelous. Those of the Giraffe and Llama 
(fig. 103) are noticeable for their great length. In the Tylo- 
poda the posterior half of the vertebrarterial canal is confluent 
with the neural canal. 

The Perissodactyla have remarkably opisthocoelous cervical 
vertebrae. Those of Jlacrauchtnia have the posterior half of 
the vertebrarterial canal confluent with the neural canal as in 
Tylopoda. In the Proboscidea they are short flattened discs 
slightly opisthocoelous ; the axis aud seventh vertebra and to 
a less extent the sixth have high neural spines. 



446 THE VERTEBRATE SKELETON. 

In the RODENTIA the atlas generally has broad wing-like 
transverse processes, and the axis a large and long neural spine, 
while the odontoid process is much developed. In the Jerboas 
(Dipus) all the cervical vertebrae except the atlas are fused 
together, a condition recalling that in armadillos. 

In the CARNIVORA the wings of the atlas are well developed 
(fig. 69, A, 1), and it is deeply cupped for articulation with 
the condyles of the skull. The axis has a long odontoid process 
and a high compressed neural spine (fig. 69, B, 4). The third 
to sixth cervical vertebrae have large transverse processes with 
prominent perforated inferior lamellae, whose ventral margins 
in the third and fourth vertebrae diverge as they pass back- 
wards, while in the fifth they are parallel and in the sixth 
convergent. The transverse processes of the seventh vertebra 
have no inferior lamellae and are not perforated. Metapo- 
physes are often developed. 

In the INSECTIVORA the cervical vertebrae vary considerably. 
The neural spines except in the case of the axis are generally 
very small and in the Shrews and Moles the neural arches 
are exceedingly slender. 

In the CHIROPTERA all the cervical vertebrae are broad and 
short with slender neural arches. 

PRIMATES. In Man the cervical vertebrae have short blunt 
transverse processes and small often bifid neural spines. The 
neural and vertebrarterial canals are large. The atlas forms 
a ring surrounding a large cavity, and has a very slender 
inferior arch and small transverse processes. Traces of a pro- 
atlas have been described in Macacus and Cynocephalus. The 
axis has a prominent spine and odontoid process and short 
transverse processes. In most Primates the cervical vertebrae 
are very similar to those of man, but the inferior lamellae of 
the transverse processes are better developed. In the Antlim 
poid Apes the neural spines are as a rule much elongated. 



THE SKELETON IN MAMMALIA. VERTEBRAL COLUMN. 447 

THORACO-LUMBAR, OR TRUNK VERTEBRAE. 

In the MONOTREMATA there are nineteen thoraco-lumbar 
vertebrae, sixteen (Echidna) or seventeen (Ornithorhynchus) 
of which bear ribs. The transverse processes are very short 
and do not articulate with the ribs, which are united to the 
centra only. 

In the MARSUPIALIA there are always nineteen thoraco- 
lumbar vertebrae, thirteen of which generally bear ribs. The 
lumbar vertebrae frequently have large metapophyses and 
anapophyses, these being specially well seen in the Kangaroos 
and Koala (Phascolarctus). 

The EDENTATA are very variable as regards their trunk 
vertebrae. The two genera of Sloths differ much as regards 
the number, for while Brady pus has only nineteen, fifteen or 
sixteen of which bear ribs, Choloepus has twenty-seven, twenty- 
four of which are thoracic, and bear ribs. In Brady pus a 
small outgrowth from the transverse process articulates with 
the neural arch of the succeeding vertebra. In both genera 
the neural spines are all directed backwards. 

In the Megatheriidae as in the sloths the neural spines 
are all directed backwards, and in the lumbar region additional 
articulating surfaces occur, better developed than are those in 
Bradypus. 

In the anteaters (Myrmecophagidae) there are seventeen 
or eighteen thoraco-lumbar vertebrae, all of which except two 
or three bear ribs. The posterior thoracic and anterior lumbar 
vertebrae articulate in a very complex fashion, second, third, and 
fourth pairs of zygapophyses being progressively developed in 
addition to the ordinary ones, as the vertebrae are followed back. 

In the Armadillos the lumbar vertebrae have long meta- 
pophyses which project upwards and forwards and help to 
support the carapace. In Glyptodon almost all the thoraco- 
lumbar vertebrae are completely ankylosed together. 

In the Manidae there are no additional zygapophyses but 
the normal ones of the lumbar and posterior thoracic regions 



448 THE VERTEBRATE SKELETON. 

are very much developed, the postzygapophyses being semi- 
cylindrical and fitting into the deep prezygapophyses of the 
succeeding vertebra. 

In the SIRENIA the number of lumbar vertebrae is very 
small ; in the dugong there are nineteen thoracic and four 
lumbar, and in the manatee seventeen thoracic and two lumbar. 

In the CETACEA the number of thoracic vertebrae varies from 
nine in Hyperoodon to fifteen or sixteen in Balaenoptera, and 
the number of lumbar vertebrae from three in Inia to twenty- 
four or more in Delphinus. The lumbar vertebrae are often 
very loosely articulated together and the zygapophyses some- 
times as in the Dolphins are placed high up on the neural 
spines. The centra are large, short in the anterior region but 
becoming longer behind. The epiphyses are prominent, and 
so are the neural spines and to a less extent the metapophyses. 
The transverse processes are well developed, anteriorly they 
arise high up on the neural arch, but when the vertebral 
column is followed back they come gradually to be placed lower 
down, till in the lumbar region they project from the middle of 
the centra. This can be well traced in the Porpoise (Phocaena). 
In the Physeteridae the transverse processes of the anterior 
thoracic vertebrae are similar to those of most Cetacea, but 
when followed back, instead of shifting their position on the 
vertebrae, they gradually disappear, and other processes 
gradually arise from the point where the capitulum of the rib 
articulates. 

UNGULATA. In the Ungulata vera the thoraco-lumbar 
vertebrae are slightly opisthocoelous. The anterior thoracic 
vertebrae commonly have exceedingly high backwardly-pro- 
jecting neural spines (fig. 89,1); but those of the lumbar and 
posterior thoracic vertebrae often point somewhat forwards 
so that the spines all converge somewhat to a point called the 
centre of motion (cp. fig. 101). In the Artiodactyla there are 
always nineteen thoraco-lumbar vertebrae, and in the Perisso- 
dactyla twenty-three. 



THE SKELETON IN MAMMALIA. VERTEBRAL COLUMN. 440 



Procama sometimes has thirty thoraco-lumbar vertebrae, a 
greater number than, occurs in any other terrestrial mammal ; 




FIG. 89. FIRST AND SECOND THORACIC VERTEBRAE OF AX Ox (Bos 
taurus) x J. (Camb. Mas. ) 



1. neural spine. 

2. neural canal. 

3. prezygapophysis. 

4. facet for articulation with the 

tuberculum of the rib. 



5. facet for articulation with the 

capitulum of the rib. 

6. postzygapophysis. 

7. foramen for exit of spinal 

nerve. 



twenty-two of these are thoracic and eight lumbar. In Phe- 
nacodus the convergence of the neural spines to a centre of 
motion is well seen. 

In the Proboscidea there are twenty-three thoraco-lumbar 
vertebrae, of which nineteen or twenty bear ribs. 

In the RODENTIA there are generally nineteen thoraco- 
lumbar vertebrae but occasionally the number rises as high as 
twenty-five. In the Hares (Leporidae) the number is nineteen, 
R. 29 



450 THE VERTEBRATE SKELETON. 

twelve or thirteen of which are thoracic. The anterior 
thoracic vertebrae have short centra and high backwardly- 
directed neural spines, the lumbar vertebrae have large for- 
wardly- and downwardly-directed transverse processes with 
expanded ends. Metapophyses, anapophyses and hypapophyses 
are all present. In the Agouti (Dasyprocta) the convergence 
of the neural spines to a centre of motion is very strongly 
marked. 

In the CARNIVORA the trunk vertebrae are nearly always 
twenty or twenty-one in number ; in the genera Felis and 
Canis thirteen of these are thoracic and seven lumbar. The 
anterior thoracic vertebrae have long backwardly-projecting 
neural spines, while the posterior thoracic and lumbar vertebrae 
have shorter and thicker neural spines which project slightly 
forwards. In the Pinnipedia there is no change in the direc- 
tion of the neural spines, and anapophyses are but little deve- 
loped. 

In the INSECTIVORA the number of trunk vertebrae varies 
much from nineteen thirteen thoracic and six lumbar in 
Tupaia, to twenty-four nineteen thoracic and five lumbar 
in Centetes. The development of the various processes varies 
in accordance with the habits of the animals, being great in 
the active forms, slight in the slowly moving or burrowing 
forms. In Talpa and Galeopithecus the intervertebral discs 
of the thoraco-lumbar region instead of being cartilaginous 
have ossified forming intercentra, a condition met with in 
very few mammals. 

In the CHIROPTERA there are seventeen or eighteen thoraco- 
lumbar vertebrae, eleven to fourteen of which may bear ribs. 
The development of processes is slight. 

Among PRIMATES the number of trunk vertebrae is gene- 
rally nineteen, of which twelve to fourteen bear ribs ; in man 
and the Gorilla and Chimpanzee the number is, however, 
seventeen, and in the Orang (Simia) sixteen. In some of the 
Lemuroidea there are as many as twenty-three or twenty-four. 






THE SKELETON IX MAMMALIA. VERTEBRAL COLUMN. 451 

In most cases the neural spines converge more or less to a 
centre of motion, and this is especially marked in some of the 
Lemurs ; it does not occur in man and the anthropoid apes. 

SACRAL AND CAUDAL VERTEBRAE. 

At the posterior end of the trunk in all mammals a 
certain number of vertebrae are found fused together forming 
the sacrum. But of these only two or three answer to the 
definition of true sacral vertebrae in being united to the ilia 
by small ribs. The others which belong to the caudal series 
may be called pseudosacral vertebrae. In different individuals 
of the same species it sometimes happens that different 
vertebrae are attached to the pelvis and form the sacrum. 
Sometimes even different vertebrae are attached to the pelvis 
at successive periods in the life history of the individual. This 
is owing to a shifting of the pelvis and has been especially 
well seen in man. In young human embryos the pelvis is 
at a certain stage attached to vertebra 30, but as develop- 
ment goes on it becomes progressively attached to the twenty- 
ninth, twenty -eighth, twenty-seventh, twenty-sixth and twenty- 
fifth vertebrae. As the attachment to these anterior vertebrae 
is gained, the attachment to the posterior ones becomes 
lost, so that in the adult the pelvis is generally attached 
to vertebrae 25 and 26. But there are no absolutely pre- 
determined sacral vertebrae, as sometimes the pelvis does not 
reach vertebra 25, remaining attached to vertebrae 26 and 27; 
sometimes it becomes attached even to vertebra 24. This 
shifting of the pelvis is seen in Choloepus in a more marked 
degree even than in man. 

Of the MOXOTREMATA, Omithorhynchus has two sacral verte- 
brae ankylosed together, while Echidna has three or four 1 . 

In MARSUPIALIA as a rule only one vertebra is directly 
united to the ilia, but one or two more are commonly fused 
to the first. In the Wombats there may be as many as four 

1 G. B. Howes, Journ. of Anat. and Phys. xxvn., p. 544. 

292 



452 THE VERTEBRATE SKELETON. 

or five vertebrae fused together in the sacral region. In 
Notary ctes there is extensive fusion in the sacral region, six 
vertebrae, owing mainly to the great development of their 
metapophyses, being united with one another, and with the 
ilia, and the greater part of the ischia. 

In most EDENTATA there is an extensive fusion of verte- 
brae in the sacral region. This is especially marked in the 
Armadillos and Megatheriidae, and to a less extent in the 
Sloths and Aard Varks. 

In the SIREXIA the vestigial pelvis is attached by ligament 
to the transverse processes of a single vertebra, which hence 
may be regarded as sacral. 

In CETACEA there is no sacrum, the vestigial pelvis not 
being connected with the vertebral column. 

In most UNGULATA the sacrum consists of one large ver- 
tebra united to the ilia, and having a varying number of 
smaller vertebrae fused with it behind. 

The same arrangement obtains in most RODENTIA, but in 
the Beavers (Castoridae) all the fused vertebrae are of much 
the same size, the posterior ones having long transverse 
processes which nearly meet the ilia. 

In CARNIVORA there may be two sacral vertebrae as in the 
Hyaena, three as in the Dog, four or five as in Bears and 
Seals. 

In INSECTIVORA from three to five are united, while in 
many CHIROPTERA all the sacral and caudal vertebrae have 
coalesced. Among PRIMATES, in Man and Anthropoid Apes 
there are usually five fused vertebrae forming the sacrum, 
but of these only two or three are connected to the ilia by ribs. 
In most of the other Anthropoidea there are two or three 
fused vertebrae, and in the Lemuroidea two to five. 

FREE CAUDAL VERTEBRAE. The free caudal vertebrae 
vary greatly in number and character. When the tail is well 
developed, the anterior vertebrae are comparatively short and 
broad, with well-developed neural arches and zygapophyses ; 



THE SKELETON IX MAMMALIA. VERTEBRAL COLUMN. 

but as the tail is followed back, the centra gradually 
lengthen and become cylindrical, and at the same time the 
neural arches and all the processes gradually become reduced 
and disappear, so that the last few vertebrae consist of simple 
rod-like centra. Chevron bones are frequently well-developed. 

Of the MONOTREMES Echidna has twelve caudal vertebrae, 
two of which bear irregular chevron bones. In Ornitho- 
rhynchus there are twenty or twenty-one caudal vertebrae with 
well-developed hypapophyses, but no chevron bones. 

In MARSUPIALS there is great diversity as regards the tail. 
In the Wombat and Koala the tail is small and without 
chevron bones. In most other Marsupials it is very long, 
having sometimes as many as thirty-five vertebrae in the 
prehensile-tailed opossums. In the Kangaroos the tail is very 
large and stout. Chevron bones are almost always present, and 
in Sotoryctes are large and expanded. 

Most EDENTATES have large tails with well -developed 
chevron bones. The length of the tail varies greatly from the 
rudimentary condition in Sloths to that in the Pangolins, one 
of which has forty-six to forty-nine caudal vertebrae the 
largest number in any known mammal. Chevron bones are 
much developed, sometimes they are Y-shaped, sometimes as in 
Priodon, they have strong diverging processes. The caudal 
vertebrae of Glyptodonts, though enclosed in a continuous 
bony sheath, have not become ankylosed together. 

The SIRENIA have numerous caudal vertebrae with wide 
transverse processes. In the CETACEA also the tail is much 
developed, and the anterior vertebrae have large chevron 
bones and prominent straight transverse processes ; the pos- 
terior caudal vertebrae, which in life are enclosed in the hori- 
zontally expanded tail fin, are without transverse processes. 

In UNGULATA the tail is simple, formed of short cylindrical 
vertebrae, which in living forms are never provided with 
chevron bones. The number of caudal vertebrae varies from 
four, sometimes met with in Procavia, to thirty-one in the 



454 THE VERTEBRATE SKELETON. 

Elephant. The tail is exceedingly long in Anoplotherium and 
in Phenacodus, in which there are thirty caudal vertebrae. 

In RODENTIA the tail is variable. In the Hares, Guinea 
pig (Cavia) and Capybara it is very small, in Pedetes and the 
Beaver it is very long and has well-developed chevron bones. 

Most of the CARNIVORA except the Bears and Seals have 
very long tails, the greatest number of vertebrae, thirty-six, 
being met with in Paradoxurus. Bears have only eight to 
ten caudal vertebrae. Chevron bones are not often much 
developed. 

In INSECTIVORA the tail is very variable as regards length, 
the number of vertebrae varying from eight in Centetes to 
forty-three in Microgale. 

In CHIROPTERA the tail is sometimes quite rudimentary, 
and as in Pteropus, composed of a few coalesced vertebrae, 
sometimes it is formed of a large number of slender ver- 
tebrae. 

In PRIMATES also the tail is very variable. In Man all 
the four caudal vertebrae are rudimentary and are fused 
together, forming the coccyx. In the Anthropoid apes, too, 
there are only four or five caudal vertebrae. In many 
monkeys of both the eastern and western hemispheres the 
tail is very long, having thirty-three vertebrae in Ateles, in 
which genus it is also prehensile. Chevron bones are present 
in all Primates with well-developed tails. In the Lemuroidea 
the number of caudal vertebrae varies from seven to twenty- 



CHAPTER XXIII. 

GENERAL ACCOUNT OF THE SKELETON IN 
MAMMALIA (CONTINUED). 

THE SKULL AND APPENDICULAR SKELETON. 

THE SKULL. 

MOXOTREMATA. In both genera the cranium is thin-walled, 
has a fairly large cavity, and is very smooth and rounded ex- 
ternally. The sutures between many of the bones early become 
obliterated in a manner comparable to that in birds, and the 
facial portion of the skull is much prolonged. 

In Echidna the face is drawn out into a gradually tapering 
rostrum, formed mainly by the premaxillae, maxillae and nasals. 
The zygomatic arch is very weak, and the palate extends very 
far back. The tympanic forms a slender ring. The mandible 
is extremely slight, with no ascending portion, and but slight 
traces of the coronoid process and angle. The hyoid has a 
wide basi-hyal and stout thyro-hyals, while the anterior cornua 
are slender, and include ossified epi-hyals and cerato-hyals. 

In Ornitharhynchus the zygomatic arch is much stouter 
than in Echidna. The face is produced into a wide beak, 
mainly supported by the premaxillae, between whose diverging 
anterior ends there is a dumb-bell-shaped bone. The maxillae 



456 



THE VERTEBRATE SKELETON. 



are flattened below, and each bears a large horny tooth, which 
meets a corresponding structure borne on a surface near the 
middle of the mandible. The mandible is considerably stouter 
than in Echidna, but the angle and coronoid process are but 
little developed. The infra-orbital foramen and the inferior 
dental and mental foramina of the mandible are all very large. 




FIG. 90. HALF FEONT viEW 1 OF THE SKULLS OF A TASMANIAN WOLF (Thy- 
lacinus cynocephalus) (to the left) x f ; AND OF A HAIKT-NOSED 
WOMBAT (Phascolomys latifrons) (to the right) x f . (Carab. Mus.) 



1. premaxilla. 

2. nasal. 

3. frontal. 

4. infra-orbital foramen. 

5. lachrymal. 

6. jugal. 



7. coronoid process of the man- 

dible. 

8. lachrymal foramen. 

i. 1. first upper incisor. 
C. canine. 



MARSUPIALIA. The skulls of the various types of the 
Marsupials frequently bear a strong superficial resemblance to 
those of some of the different groups of placental main] na Is. 
Thus the skull of the Dasyuridae resembles that of the Carni- 
vora, the resemblance being most marked between the skulls of 



1 The figure was drawn from a photograph and the size of the jaws 
relatively to the cranium is exaggerated. 



THE SKELETON IX MAMMALIA. THE SKULL. 457 

Thylacimis and the dog. The skull of Notoryctes is strongly sug- 
gestive of that of an Insectivore, and that of other Marsupials 
such as the wombat, recalls equally the characteristic features 
of a Rodent's skull. But, however much they may differ from 
one another, the skulls of all Marsupials agree in the following 
respects. (1) The brain cavity, and especially the cerebral 
fossa, has a very small comparative size. (2) The nasals are 
always large, and the mesethmoid is extensively ossified, and 
terminated by a prominent vertical edge. (3) Processes from 
the jugal and frontal in living forms never meet and enclose 
the orbit, but the zygomatic arch is always complete. (4) The 
jugal always extends back to form part of the glenoid fossa. 
(5) The lachrymal canal opens either external to or upon the 
margin of the orbit, and the nasal processes of the premaxillae 
never quite reach the f rentals. (6) The posterior part of the 
palate is commonly pierced by large oval vacuities. (7) The 
tympanic is small and never fused to the bones of the 
cranium. (8) The carotid canal perforates the basisphenoid 
and not the tympanic bulla. (9) The optic foramen and 
sphenoidal fissure are confluent. (10) In every case except 
Tarsipes the angle of the mandible is more or less inflected. 

The skull of the extinct Thylacoleo differs from that of all 
other Marsupials in the fact that the postorbital bar is com- 
plete. The hyoid is constructed on much the same plan in all 
Marsupials. It consists of a small basi-hyal, a pair of broad 
cerato-hyals, and a pair of strong thyro-hyals. The epi-hyals 
and stylo-hyals are generally unossitied. 

EDENTATA. In Sloths ( Brady podidae) the sutures become 
early obliterated, the cranial portion of the skull is rather 
high, and the facial portion very short. The lachrymal is very 
small, and its canal opens outside the orbit. The zygomatic 
arch is incomplete, and the jugal (fig. 91, 5) is curiously forked, 
but in a manner differing in the two genera. The premaxillae 
are very small, in Bradypus quite vestigial. The mandible is 
well developed, the angle being specially marked in Bradypus. 



458 



THE VERTEBRATE SKELETON. 



In Choloepus the symphysial part is drawn out in a somewhat 
spout-like manner (fig. 91, 6). In both genera the thyro-hyals 
are ankylosed with the basi-hyal. 




FIG. 91. SKULL OF A TWO-FINGERED SLOTH (Choloepus didactylus) x \. 
(Camb. Mus.) 

1. anterior nares. 4. angle of the mandible. 

2. postorbital process of the 5. jugal. 

frontal. 6. spout-like prolongation of the 

3. coronoid process. mandible. 

In Megatherium the general appearance of the skull is 
distinctly sloth-like, but the facial portion is more elongated, 
partly owing to the development of a prenasal bone, and the 
zygomatic arch is complete. The mandible is very deep in the 
middle, and is drawn out into a long spout-like process in front. 

Anteaters (Myrmecophagidae) have a much modified skull, 
and this is especially the case in the Great Anteater, Myrme- 
cophaga. The skull is smooth and evenly-rounded, in these 
respects recalling that of Echidna, but it is longer and tapers 
much more gradually than in Echidna. The occipital condyles 
are remarkably large. The premaxillae are small, and the 
long rostrum is chiefly composed of the maxillae and nasals 
with the mesethmoid and vomer. The zygomatic arch is 
incomplete, and there is no trace of a separation between the 
orbit and the temporal fossa. The palate is much elongated, 



THE SKELETON IN MAMMALIA. THE SKULL. 459 

the pterygoids meeting in the middle line just like the pala- 
tines. The mandible is very long and slender, there being no 
definite coronoid process, and a short and slight symphysis. 
The hyoid arch is noticeable for the length of the anterior 
cornu. 

In the Armadillos (Dasypodidae) the skull varies a good 
deal in shape, but the facial portion is always tapering and 
depressed. The zygomatic arch is complete. In Dasypus and 
Chlamydophorus the tympanic bulla is well ossified. 

In the Glyptodontidae the skull is very short and deep ; 
the zygomatic arch is complete, and has a long downwardly 
projecting maxillary process. The mandible is massive, and 
has a very high ascending portion. 

In the Manidae the skull is smooth and rounded, the zygo- 
matic arch is incomplete, and the orbit is inconspicuous. The 
palate is long and narrow, but the pterygoids do not take part- 
in its formation. The mandible is slightly developed and has 
no angle or coronoid process. 

In Orycteropvjs the zygomatic arch is complete, and there 
is a small postorbital process to the frontal. The mandible is 
well-developed, having a coronoid process and definite ascending 
portion, and the hyoid is well ossified. 

SIRENIA. The skull, and especially the brain case of all 
Sirenia, is remarkable for the general density of the component 
bones, which, though often very thick, are without air sinuses. 
It is noticeable also for the roughness of the bones, and the 
irregular manner in which they are united together. 

The cranial cavity is decidedly small, the reduction being 
specially noticeable in the cerebral fossa, which is not much 
larger than the cerebellar fossa. The foramen magnum is 
large, and the dorsal surface of the cranium narrow. The 
zygomatic arch is very strongly developed, the squamosal (fig. 
92, -4) being especially prominent, and being drawn out not only 
into the zygomatic process, but also into a large post-tympanic 
process which articulates with the exoccipital. At the side 



460 



THE VERTEBRATE SKELETON. 



of the skull between the squamosal, supra-occipital and exocci- 
pital, there is a wide vacuity in the cranial wall, partially filled 



.--5 




FIG. 92. LATERAL VIEW OF THE SKULL OF Rhytina stelleri x i. 
(Brit. Mus.) 

7. pterygoid process of the ali- 
sphenoid. 



frontal, 
parietal, 
zygomatic process 

squamosal. 
squamosal. 
exoccipital. 
occipital condyle. 



of the 8. jugal. 

9. premaxilla. 

10. angle of the mandible. 

11. maxilla. 



up by the very large periotic, which is ankylosed to the tym- 
panic, but is not united to any other bones of the skull. The 
foramen lacerum medium is confluent with the foramen lacerum 
anterius, and the two together form an enormous vacuity on 
the floor of the skull, bounded chiefly by the exoccipital, basi- 
occipital, alisphenoid and squamosal. The jugal (fig. 92, 8) is 
large and in Manatus sends up a strong process, which nearly 
or quite meets the postorbital process of the frontal, completing 
the orbit. In the other Sirenia the orbit is completely confluent 
with the very large temporal fossa. The lachrymal in M until* 
is very small, but is larger in Halicore. The premaxillae (fig. 
92, 9) are large, but smaller in Manatus than in the other 



THE SKELETON IX MAMMALIA. THE SKULL. 461 

genera, in all of which they are curiously bent down in front. 
Their upper margin forms the anterior border of a very large 
aperture lying high on the roof of the skull and extending 
back for a considerable distance. This aperture is formed by 
the union of the two anterior nares. The nasals are quite 
vestigial or absent, and the narial aperture is bounded above 
by the frontals ; in its floor are seen the slender vomer and 
large mesethmoid. The palate is long and narrow, and formed 
mainly by the maxillae ; behind it there is a large irregular 
process formed by the union of the palatine, pterygoid, and 
pterygoid plate of the alisphenoid. The mandible is very 
massive and has a very high ascending portion, a rounded 
angle (fig. 92, 10), and a prominent coronoid process ; the two 
rami are firmly ankylosed together. The hyoid consists prin- 
cipally of the broad flat basi-hyal ; the anterior cornua are but 
slightly ossified, while the thyro-hyals are not ossified at alL 

CETACEA. The skull in all Cetacea, especially in the Odon- 
toceti, is a good deal modified from the ordinary mammalian 
type. 

In the ARCHAEOCETI this modification is less marked than 
in either of the other suborders. The nasals and premaxillae 
are a good deal larger than they are in living forms, and the 
anterior nares are placed further forward. The maxillae do 
not extend back over the frontals, and there is a well-marked 
sagittal crest. 

In the MTSTACOCETI the skull is always quite bilaterally 
>.yiu metrical, and is not so much modified from the ordinary 
mammalian type as in the Odontoceti. The parietals are not, 
as in the Odontoceti, separated by a wide interparietal, but 
meet ; they are, however, hidden under the very large supra- 
occipital. The nasals are developed to a certain extent, and 
the nares, though placed very far back and near the top of the 
head, terminate forwardly-directed narial passages. Turbinal 
bones are also developed to some extent ; this fact, and the 
occurrence of a definite though small olfactory fossa constituting 



462 THE VERTEBRATE SKELETON. 

important distinctions from the Odontoceti. The maxillae are 
large, but do not extend back to cover the frontals as in the 
Odontoceti. The zygomatic process of the squamosal is very 
large. The mandibular rarni are not compressed, but are 
rounded and arched outwards, and never meet in a long 
symphysis. 

ODONTOCETI. The skull departs widely from the ordinary 
mammalian type. The following description will apply to any 
of the following genera of the Delphinidae, Phocaena, Globi- 
cephalus, Lagenorhynchus, Delphinus, Tursiops, Prodelphinus, 
Sotalia. 

The upper surface of the skull is more or less asymmetrical. 
The cerebral cavity is high, short and broad; and formed mainly 
by the cerebral fossa, the olfactory fossa being entirely absent. 
The supra-occipital (fig. 93, 3) is very large, and forms much 
of the posterior part of the roof of the skull. It has the 
interparietal (fig. 93, 7) fused with it, and completely separates 
the two parietals. The frontal (tig. 93, 10) is large and late- 
rally expanded, forming the roof of the orbit, but is almost 
completely covered by an extension of the maxilla. The 
zygomatic arch is very slender, and is mainly formed by a 
rod-like process from the jugal (fig. 93, 15), the zygomatic 
process of the squamosal being short and stout. 

The nasal passages are peculiarly modified, instead of 
passing horizontally forwards above the roof of the mouth, 
they pass upwards and even somewhat backwards towards 
the top of the skull (fig. 93, 23). They are bounded laterally 
by two processes from the premaxillae, the left of which is 
shorter than the right. The nasal cavities are narrow and 
without turbinals and the nasals (fig. 93, 19) are almost as 
much reduced as in Siren ia. 

In front of the nasal openings the face is prolonged as ;i 
narrow beak or rostrum of varying length, formed by the 
maxillae and premaxillae surrounding the vomer and large 
mesethmoid (tig. 93, 11), which sends forwards a long partially 



THE SKELETON IN MAMMALIA. THE SKULL. 463 



,3 




18 



FIG. 93. A, LATERAL VIEW, AND B, LONGITUDINAL SECTION OF THE SKULL 
OF A YOUNG CA'ING WHALE (Globicephalus melas) x $. (Brit. Mus. 

1. basi-occipitaL 13. periotic. 

2. exoccipital. 14. squamosal. 

3. supra-occipital. 15. jugal. 

4. basisphenoid. 16. vomer. 

5. alisphenoid. 17. palatine. 

6. parietal. 18. pterygoid. 

7. interparietal. 19. nasal. 

8. presphenoid. 20. maxilla. 

9. orbitosphenoid. 21. premaxilla. 

10. frontal. '22. mandible. 

11. mesethmoid. 23. anterior nares. 

12. tympanic. 



464 THE VERTEBRATE SKELETON. 

cartilaginous process, and is fused behind with the presphenoid 
(fig. 93, 8). The basi-occipital (fig. 93, 1) too is fused with 
the basisphenoid. The foramen rotunduni is confluent with 
the sphenoidal fissure, and the foramen ovale with the foramen 
lacerum medium and the foramen lacerum posterius. The 
palate is mainly formed by the maxillae ; the premaxillae and 
palatines (fig. 93, 17), though both meet in symphyses, forming 
very little of it. The pterygoids vary in size in the different 
genera, sometimes as in Lagenorhynchus and Delphinus meet- 
ing in the middle line, sometimes as in Phocaena and Globi- 
cephalus (fig. 93, 18) being widely separated. The tympanic 
and periotic are not fused together, and the periotic has 
generally no bony union with the rest of the skull. The 
mandible is rather slightly developed, with the rami straight, 
compressed and tapering to the anterior end. The condyle is 
not raised at all above the edge of the ramus ; the angle is 
rounded and the coronoid process is very small. Platanista has 
a curiously modified skull ; the rostrum and mandible are 
exceedingly long and narrow, and arising from the maxillae 
are two great plates of bone which nearly meet above. 

In the Physeteridae the skull is raised into a very promi- 
nent crest at the vertex behind the nares. In front of this 
in Hyperoodon a pair of ridges occur, formed by outgrowths 
from the maxillae. In the old male these ridges reach an 
enormous size and almost meet in the middle line. In Phy- 
seter, the Sperm whale, these ridges are not developed ; the 
maxillae and premaxillae unite with the other bones of the 
crest enclosing an enormous half basin-shaped cavity, at the 
base of which are the very asymmetrical anterior narial aper- 
tures. 

In all living Cetacea the hyoid has the same general shape, 
consisting firstly of a crescentic bone formed by the fusion 
of the thyro-hyals with the basi-hyal, and secondly of the 
anterior cornu formed principally by the strong stylo-hyal. 

UNGULATA. None of the distinctive characters separating 



THE SKELETON IX MAMMALIA. THE SKULL. 465 

the Ungulata from the other groups of mammals are drawn 
from the skull. But in the Ungulata vera as opposed to the 
Subungulata a distinguishing feature is found in the fact that 
the lachrymal and jugal form a considerable part of the side 
of the face, and that the jugal always forms the anterior part 
of the zygomatic arch, the maxilla taking no part in it. 

UXGI'LATA VERA. 

ARTIODACTYLA. The skull in Artiodactyla differs from that 
in Perissodactyla in the fact that the posterior end of the 
nasal is not expanded and there is no alisphenoid canal. 

The skulls in the different groups of Artiodactyla differ 
considerably from one another. 

The skull of the Pig 1 will be described as illustrative of the 
skull in the Suina. In the Pig as in most Artiodactyla the 
face is bent sharply down on the basicranial axis, the com- 
mencement of the vomer being situated below the mesethmoid 
instead of in front of it as in most skulls. The occipital region 
of the skull is small, and the line of junction of the supra-occi- 
pital and parietals is raised into a prominent occipital crest. 
The parietal completely fuses at an early stage with its fellow, 
and the exoccipital is drawn out into a long paroccipital process 
(fig. 94, A, 8). The frontal is large and broad and drawn out 
into a small postorbital process. The lachrymal too is large and 
takes a considerable part in forming the side of the face in front 
of the orbit, as does also the jugal, though to a less extent. 
The face is long and tapers much anteriorly. The nasals are 
long and narrow, as are the nasal processes of the premaxillae, 
which do not however reach the frontals. A prenasal ossicle 
is developed in front of the mesethmoid. The palate is long 
and narrow, the pterygoid (fig. 94, A, 10) is small, but the 
pterygoid process of the alisphenoid is prominent. The 
squamosal is small and has the tympanic fused with it ; the 
tympanic is dilated below, forming a bulla (fig. 94, A, 9) filled 

1 See W. K. Parker, "On the Structure and Development of the Skull 
in the Pig." Phil. Trans, pp. 289336, 1874. 

R. 30 



466 



THE VERTEBRATE SKELETON. 




FIG. 94. A, CRANIUM AND 

1. jugal. 

2. postorbital process of 

frontal. 

3. zygomatic process of 

squamosal. 

4. supra-occipital. 

5. glenoid cavity. 

6. occipital condyle. 

7. foramen magnum. 

8. paroccipital process of 

exoccipital. 

9. tympanic bulla. 
10. pterygoid. 



B, MANDIBLE OF A PlG (SllS SCrofd) X } . 

(Camb. Mus.) 

11. anterior palatine foramen, 
the 12. palatal plate of maxilla. 

13. coronoid process. 
the 14. mandibular condyle. 

i 1, i 2, 3. first, second, and third 

incisors, 
c. canine. 

pm 1, pm 2, pin 3, pm 4. first, 
second, third, and fourth 
the premolars. 

ml, m2, m3. first, second, and 
third molars. 



THE SKELETON IN MAMMALIA. THE SKULL. 

with cancellous bone, and above forms the floor of a long up- 
wardly-directed auditory meatus. The mandible has a high 
ascending portion and a small coronoid process (fig. 94, B, 13). 
The hyoid differs from that of most Ungulates, the stylo-hyal 
being very imperfectly ossified. 

In Hippopotamus the skull though essentially like that of 
the pig is much modified in detail. The brain cavity is very 
small, while the jaws are immensely developed. The face con- 
tracts in front of the orbits and then expands again greatly, 
to lodge the enormous incisor and canine teeth. The postorbital 
bar is complete or nearly so, and the orbits project curiously 
outwards and slightly upwards : the lachrymal is thin and 




FIG. 95. MAXDIBLE OF A HIPPOPOTAMUS (H. amphibius) x f . 
(Camb. Mus.) 

The second incisor of the left side is missing and the crowns of the 
grinding teeth are much worn. 

1. condyle. c. canine. 

2. coronoid process. pm 3. third premolar. 

3. mental foramina. m 1, HJ 3. first and third molar, 
i 1, i 2." first and second incisors. 

302 



468 THE VERTEBKATE SKELETON. 

much dilated. The squamosal is drawn out into a postglenoid 
process, and the hamular process of the pterygoid is prominent. 
The tympanic bulla is filled with cancellous bone. The mandible 
is enormously large, the symphysis is long, the angle much 
expanded and drawn out into a process which projects outwards 
and forwards. k 

Among extinct forms related to the Suina, Cyclopidius is 
noticeable for having large vacuities in the lachry mo-nasal 
region, while Cotylops has the postorbital bar complete ; both 
these forms are from the North American Miocene. 

In the Tylopoda and Tragulina the skull resembles in most 
respects that of the Ruminants, shortly to be described ; but it 
is allied to that of the Suina in having the tympanic bulla tilled 
with cancellous bone. The tympanic bulla is better developed 
in the Tragulina than in most Ungulates. 

Among Ruminants, the Bovidae, that large group includ- 
ing the Oxen, Sheep, and Antelopes, as a rule have the face 
bent on the basicranial axis much as in the Suina. The 
parietals are generally small and early coalesce, the frontals 
are large and are usually drawn out into horn cores, which are 
however absent in the skulls of some domestic varieties of sheep 
and oxen, and also in some of the earlier extinct forms of Bo- 
vidae. These horn cores are formed internally of cancellous 
bone, and on them the true epidermal horns are borne. In 
young animals there is a distinct interparietal, but this early 
fuses with the supra-occipital, and in the oxen also with the 
parietals. The occipital crest is generally well marked, but 
in the genus Bos becomes merged in a very prominent straight 
ridge running between the two horn cores ; this ridge, which 
contains air cells communicating with those in the horn cores, is 
not nearly so well marked in Bison. There is often, as in Gazella, 
a vacuity on the side of the face between the nasal, frontal, 
lachrymal, and maxilla, but this is not found in oxen or sheep. 
The premaxillae are small, the nasals |ire long and pointed, 
and the turbinals are much developed. The Saiga antelope 



THE SKELETON IN MAMMALIA. THE SKULL. 469 

has a curiously specialised skull ; the nasals are absent or 
have coalesced with the frontals and the anterior nares are 
enormously large. In all Ruminants the lachrymal is large 
and forms a considerable part of the side of the face ; it often 
bears a considerable depression, the suborbital or lachrymal 
fossa, well seen in most of the smaller antelopes. The post- 
orbital bar is complete, and the orbit is prominent and nearly 
circular. The palatines and pterygoids are moderately large, 
and the pterygoids have a back wardly-projec ting hamular pro- 
cess. The squamosal is small, but has a postglenoid process. 
The tympanic is not fused to the periotic and has a small bulla 
not filled with cancellous bone. There is a large paroccipital 
process to the exoccipital and the mandible has a long slender 
coronoid process. 

In the Cervidae and Giraffidae the face is not bent down 
on the basicranial axis as it is in the Bovidae. The frontals are 
drawn out, not into permanent horn cores as in the Bovidae, 
but into short outgrowths, the pedicels, upon which in the 
Cervidae long antlers are annually developed. These antlers are 
outgrowths of bone, and are covered during development by 
vascular integument, which dries up and peels off when growth 
is complete. Every year they are detached, by a process of 
absorption at the base, and shed. They may occur in both sexes, 
as in the Reindeer, but as a rule they are found only in the 
male. They are generally more or less branched, and are some- 
times of enormous size and weight, as in the extinct Cermis mega- 
ceros. In young animals they are always simple, but become 
annually more and more complicated as the animal grows older. 

In the Giraffe the frontals bear a small pair of bony cores, 
which are at first distinct, but subsequently become fused to 
the skull. In the allied Sivatfierium, a very large form from 
the Indian Pliocene, the skull bears two pairs of bony out- 
growths, a pair of short conical outgrowths above the orbits, 
and a pair of large expanded outgrowths on the occiput. 

The opening of the lachrymal canal is commonly double 



470 THE VERTEBRATE SKELETON. 

and the lachrymal fossa is large in the Cervidae and the Giraf- 
fidae except Sivatherium. The vacuity between the frontal, 
lachrymal, maxilla, and nasal is specially large. 

The hyoid of Ruminants is noticeable for the development 
of the anterior cornua, which include stout and short cerato- 
hyals and epi-hyals, long and strong stylo-hyals and large 
tympano-hyals which are more or less imbedded in the tym- 
panics. 

PERISSODACTYLA. In the skull of Perissodactyles an ali- 
sphenoid canal is found and the nasals are expanded behind. 
Among the living animals belonging to this group the skull least 
modified from the ordinary type is that in Rhinoceros. In this 
form the skull is considerably elongated, the facial portion being 
very large. The occipital region is elevated, but the cranial 
cavity is small, the boundary line between the occipital and 
parietal regions being drawn out into a prominent crest, which 
is occupied by air cells. There is no postorbital process to the 
frontal, and the orbit is completely confluent with the temporal 
fossa. The nasals are fused together and are very strongly 
developed, extending far forwards, sometimes considerably 
beyond the premaxillae. In some extinct species, such as Elas- 
motherium and the Tichorhine Rhinoceros, R. antiquitatis, the 
mesethmoid is ossified as far forwards as the end of the nasals. 
The nasals are arched and bear one or two roughened surfaces 
to which the great nasal horns are attached. The premaxillae 
are very small and the pterygoids are slender. The palate is 
long, narrow, and deeply excavated behind. The postglenoid 
process of the squamosal is well developed, and generally 
longer than the paroccipital process of the exoccipital. The 
tympanic and periotic are both small and are fused together. 
The condyle of the mandible is very wide, the angle rounded, 
and the coronoid process moderately developed. 

In the Titanotheriidae, a family of extinct Perissodactyla 
from the Miocene of North America, the occipital region is much 
elevated, as is also the fronto-nasal region, the nasals (perhaps 



THE SKELETON IN MAMMALIA. THE SKULL. 471 

only in the male) bearing a pair of blunt bony outgrowths. 
Between these two elevated regions the skull is much de- 
<1. The cranial cavity is very small, the orbit confluent 
with the temporal fossa, and the zygomatic arch massive. 

In Tapirus the orbit and temporal fossa are confluent. 
The nasals are small, wide behind and pointed in front, and 
are supported by the mesethmoid ; the anterior nares are 
exceedingly large and their lateral boundaries are entirely 
formed by the maxillae. The postglenoid and post-tympanic 
processes of the squamosal are large. The periotic is not fused 
to the squamosal or to the small tympanic. The mandible is 
large and has the angle much developed and somewhat inflected. 

Palaeotherium, which lived in early Tertiary times, has a 
skull much like that of the Tapir, especially as regards the 
nasal bones. 

In the Horse and its allies (Equidae) the facial portion of 
the skull is very large as compared with the cranial portion, 
the nasals and nasal cavities being specially large. In the 
living species of the genus Equus there is no fossa between the 
maxilla and lachrymal, but it occurs in some extinct species. 
The lachrymal and jugal form a considerable part of the side 
of the face ; and the orbit though small is complete and pro- 
minent. The postorbital bar is formed by a strong outgrowth 
from the frontal, which unites with a forward extension of the 
squamosal. The squamosal may extend forwards and form 
part of the wall of the orbit, a very unusual feature, as in most 
mammals the squamosal stops before the postorbital bar. The 
palate is narrow and excavated behind as in Rhinoceros ; the 
palatines take very little part in its formation. The glenoid 
surface for the articulation of the mandible is very wide. The 
squamosal gives rise to small postglenoid and post-tympanic 
processes, and the exoccipital to a large paroccipital process. 
The tympanic and periotic are ankylosed together, but not to 
any other bones. 

In the SUBUNGULATA, the lachrymal and jugal do not form 



472 THE VERTEBRATE SKELETON. 

any considerable part of the side of the face, and the maxilla 
commonly takes part in the formation of the zygomatic arch. 

TOXODONTIA. The skull in the Toxodontia shows several 
Artiodactyloid features, while the manus and pes are of a more 
Perissodactyloid type. The Artiodactyloid features are (1) the 
absence of an alisphenoid canal, (2) the fact that the palate is 
not excavated behind, and that the palatines form a consider- 
able part of it, and (3) the fusion of the tympanic to the 
squamosal and exoccipital, forming the floor of an upwardly 
directed auditory meatus. The frontal has a fairly well deve- 
loped postorbital process, but the orbit is confluent with the 
temporal fossa. The premaxilla is well developed, as is the par- 
occipital process of the exoccipital, especially in Typotherium. 
The mandible has a rounded angle and a coronoid process of 
moderate size. In Typotherium the ascending portion is very 
massive. 

CONDYLARTHRA. As far as is known the skull of these 
generalised Ungulates is depressed, and is frequently marked 
by a strong sagittal crest. The cranial cavity is small, the 
cerebral fossa in Phenacodus being exceptionally small. The 
orbit is completely confluent with the temporal fossa. 

HYRACOIDEA. The skull of Procavia resembles that of 
Perissodactyles more than that of any other Ungulates, but 
differs strongly in the comparatively small size of its facial 
portion. The posterior portion of the cranium is rather high, 
the occipital plane being nearly vertical. There is a small 
interparietal. The nasals are wide behind, and the zygomatic 
arch is strongly developed, its most anterior part being formed 
by the maxilla. The jugal and parietal give rise to post- 
orbital processes which sometimes meet, but as a rule the orbit 
is confluent with the temporal fossa ; it is very uncommon 
for the parietal to give rise to a postorbital process, and even 
in Procavia the frontal often forms part of the process. The 
alisphenoid canal, and postglenoid and paroccipital processes 
are well developed. The tympanic bulla is large and the 



THE SKELETON IN MAMMALIA. THE SKULL. 473 

periotic and tympanic are fused together, but not as a rule 
to the squamosal. The ascending portion of the mandible is 
very high and broad, the angle rounded and the coronoid 
process moderate in size. The hyoid is singular, there is a 
large flat basi-hyal prolonged laterally into two broad flattened 
thyro-hyals. Articulating with its anterior end are two large 
triangular cerato-hyals, which are drawn out into two processes 
meeting in the middle line. 

AMBLYPODA. In the Uintatheriidae (Dinocerata) the skull 
has a very remarkable character, being long and narrow and 
drawn out into three pairs of rounded protuberances, a small 
pair on the nasals, a larger pair on the maxillae in front of the 
orbits, and the largest pair on the parietals. The cranial cavity, 
and especially the cerebral fossa, is extraordinarily small. The 
orbit is not divided behind from the temporal fossa. The 
mandible has a prominent angle, and a long curved coronoid 
process ; its symphysial portion bears a curious flattened out- 
growth to protect the great upper canines. 

In Coryphodon the skull is of a more normal character, 
being without the conspicuous protuberances. The cranial 
cavity though very small is not so small as in Uintatherium. 

PROBOSCIDEA. The character of the skull in the young ele- 
phant differs much from that in the old animal. In very young 
individuals the skull is of a normal character, and the cranial 
cavity is distinctly large in proportion to the bulk of the skull. 
But as the animal gets older, while its brain does not grow 
much, the size of its trunk and especially of its tusks increases 
greatly ; and consequently the skull wall is required to be of 
very great superficial extent in order to afford space for the 
attachment of the muscles necessary for the support of these 
heavy weights. This increase in superficial extent is brought 
about without much increase in weight of bone by the develop- 
ment of an enormous number of air cells in nearly all the 
bones of the skull ; sometimes, as in the case of the frontal, 
separating the inner wall of the bone from the outer, by as 



474 



THE VERTEBRATE SKELETON. 



much as a foot. This development of air cells is accompanied 
by the obliteration of the sutures between the various bones. 
The most noticeable point with regard to the cranial cavity 
is the comparatively large size of the olfactory fossa. The 
supra-occipital (figs. 96 and 97, 9) is large exceedingly large 
in the adult skull; the parietals (figs. 96 and 97, 2) are also 
very large. The frontals send out small postorbital processes, 
but these do not meet processes from the small jugal, which 



,14 




11 



FIG. 96. SKULL OF A YOUNG INDIAN ELEPHANT (Elephas indicus), SEEN 

FROM THE BIGHT SIDE, THE BOOTS OF THE TEETH HAVE BEEN EXPOSED. 

x^. (Camb. Mus.) 

1. exoccipital. 

2. parietal. 

3. frontal. 

4. squamosal. 

5. jugal. 

6. premaxilla. 

7. maxilla. 

9. supra-occipital. 
13. basi-occipital. 



14. postorbital process of the 

frontal. 

15. lachrymal. 

16. pterygoid process of the ali- 

sphenoid. 
i 1. incisor. 
mm 3., mm 4. third and fourth 

milk molars. 
ml. first molar. 



THE SKELETON IX MAMMALIA. THE SKULL. 



475 



forms only the middle part of the slender zygomatic arch, the 
anterior part being formed by the maxilla. The lachrymal 
(fig. 96, 15) is small and lies almost entirely inside the orbit. 
The anterior narial aperture (fig. 97, 8) is wide and directed 
upwards, opening high on the anterior surface of the skull. It 
is bounded above by the short thick nasals and below by the 
premaxillae. The narial passage is freely open, maxillo-tur- 
binals not being developed. The palatine is well developed, 
the pterygoid is small and early fuses with the pterygoid 

2 



17 



10 




mm4 



FlG. 97. LONGITUDINAL SECTION TAKEN BATHER TO THE BIGHT OF THE 
MIDDLE LINE OF THE SKULL OF A YOUNG INDIAN ELEPHANT (E. 

Indicus) x . (Camb. Mas.) 
8. 
10. 



11. 



anterior nares. 

periotic. 

palatine. 



12. pterygoid. 

17. nasal. 

Other numbers as in Fig. 96. 



process of the alisphenoid. The tympanic is united with the 
periotic but not with the squamosal, and forms a large auditory 



476 THE VERTEBRATE SKELETON. 

bulla. There are no paroccipital or postglenoid processes. 
The exoccipital is not perforated by the condylar foramen, a 
very exceptional condition. 

The mandible has a high ascending portion, is rounded off 
below and has no angle. The symphysial portion is long, 
narrow, and spout-like, and the coronoid process is small. 
The thyro-hyals are ankylosed with the basi-hyal, which is 
connected with the large forked stylo-hyals by ligament only. 

RODENTIA. The cranial cavity is depressed, elongated, and 
rather small, and the cerebral fossa lies entirely in front of the 
cerebellar fossa. The occipital plane is vertical or directed 
somewhat backwards, and the supra-occipital does not form 
much of the roof of the cranium. The paroccipital processes 
of the exoccipitals are generally of moderate size ; in the 
Capybara (Hydrochaerus), however, they are very long, and 
are laterally compressed and directed forwards. The parietals 
are small, and often become co'mpletely fused together ; there 
is sometimes a small interparietal. The frontals in most genera 
have no trace of a postorbital process ; in Squirrels, Marmots 
and Hares, however, one occurs, but in no case does it meet a 
corresponding process from the zygomatic arch, so the orbit 
and temporal fossa are completely confluent. In Hares the 
postorbital process of the frontal is much flattened, and has 
an irregular margin. The temporal fossa is always small, and 
in Lophiomys is arched over by plates arising respectively 
from the parietal and jugal ; a secondary roof is thus partially 
developed in a manner unique among mammals, but carried 
to a great extent in many Chelonia. The nasal bones and 
cavities are large, attaining their maximum development in 
the Porcupines (fig. 98, 1). The premaxilla is always very 
large, and sends back a long process which meets the frontal. 
The vomer is occasionally found persisting in two separate 
halves, a feature recalling the arrangement in Sauropsids. In 
many Rodents there is an enormous vacuity at the base of the 
maxillary portion of the zygomatic arch. It is sometimes as 



THE SKELETON IN MAMMALIA. THE SKULL. 4 < , 

large as the orbit, and attains its maximum development in 
the Capybara and other Hystricomorpha ; in the Marmots, 
Beavers, and Squirrels (Sciuromorpha), and in the Hares it is 
undeveloped. In Lagostomus the maxilla bears an upwardly 
directed plate of bone, shutting off from this vacuity a space 
which is the true infra-orbital foramen. 

The zygomatic arch is always complete, and in many cases 
the jugal extends back to form part at least of the glenoid 




-3 



FlG. 98. HAT.F FBOXT VIEW OF THE SKULL OF A PORCUPINE 

(Hystrix cristata) x $ . (Camb. Mus.) 

1. nasal. 5. premaxilla. 

2. niaxillo-turbinals. 6. jugal. 

3. infra-orbital vacuity. i 1. upper incisor. 

4. maxilla. 

surface for articulation with the mandible. In Codogenys the 
jugal and maxillary portion of the zygomatic arch is greatly 
expanded and roughened, and the maxillary portion encloses a 
large cavity. The palate in Rodents is narrow, and the space 
between the incisor and molar teeth passes imperceptibly 
into the sides of the face. The anterior palatine foramina 
form long, rather narrow slits in this region. The bony 
palate between the grinding teeth is sometimes as in the Hares 



478 THE VERTEBRATE SKELETON. 

very short, sometimes as in the Capybara very long. The 
maxilla extends back beneath the orbit to unite with the 
squamosal. The pterygoid is always small, but sometimes 
has a well-marked hamular process which in Hystrix, Lagos- 
tomus, and some other genera unites with the tympanic bulla. 
The periotic is large, and fused with the tympanic, which 
forms a prominent bulla, and is generally drawn out into a 
tubular meatus. The bulla attains its maximum development 
in Chinchilla and Dipus. 

The mandible is narrow and rounded in front, the two 
halves meeting in a long symphysis. The angle is generally 
drawn out into a long backwardly-projecting process, which is 
often pointed and directed upwards. In the Hares the angle 
is rounded. The coronoid process is never large. 

There are a number of points in which the skull of the 
Duplicidentata (Hares and Babbits) differs from that of other 
Rodents, (a) The sutures between the basi-occipital and 
basisphenoid, and between the basisphenoid and presphenoid 
remain open throughout life. (6) Much of the maxilla forming 
the side of the face in front of the orbit is fenestrated. (c) The 
optic foramina are united to form a single hole, much as in 
birds, (d) The coronoid process is slightly differentiated from 
the ascending portion of the mandible. The first two of these 
points have been thought to indicate degradation of the 
hares and rabbits as compared with higher mammals. 

CARNIVORA 1 . It is characteristic of the skull in Carnivora 
that the glenoid fossa is deep, and the postglenoid process 
(fig. 75, 23) well developed. The condyle of the mandible is 
much elongated transversely. The orbit and temporal fossa 
in the great majority of forms communicate freely, the post- 
orbital bar being incomplete. 

CARNIVORA VERA. The axis of the facial portion of the 
skull is a direct continuation of that of the cranial portion. 

1 See W. H. Flower, "On the value of the characters of the base of the 
cranium in the classification of the order Carnivora." P. Z^ S. 1869, p. 5. 



THE SKELETON IX MAMMALIA. THE SKULL. 479 

The cranial cavity though rather depressed is large, and 
generally long, though in Cats it is comparatively short and 
wide. The occipital plane is nearly vertical^ and the exocci- 
pitals are developed into fairly prominent paroccipital processes. 
The interparietal is commonly distinct, and the parietals unite 
in a long sagittal suture, which is often developed into a crest. 
The nasals (fig. 73, 4) are well developed, especially in Cats, and 
the nasal processes of the premaxillae do not nearly reach the 
frontals. A considerable part of the palate is formed by the 
palatine, and the maxillary portion is pierced by rather long 
anterior palatine foramina. The pterygoid has a hamnlar 
process. The zygomatic arch is strong, especially in Cats. 
Postorbital processes are developed on the frontal (fig. 73, 
10) and jugal, but never form a complete postorbital bar. A 
carotid canal is well seen in the Ursidae, and to a less extent 
in the Felidae ; in the Canidae there is an alisphenoid canal 
(fig. 75, 21). 

The auditory bulla differs a good deal in the different 
groups. In the Bears (Ursidae) it is not much inflated, and 
is most prominent along its inner border ; it is not closely con- 
nected with the paroccipital process. In the Cats it is very 
prominent, and its cavity is almost divided by a septum into 
two parts, the inner of which contains the auditory ossicles. 
The paroccipital process is closely applied to the bulla. In the 
Dogs the bulla is intermediate in character between that of 
the Cats and that of the Bears ; it is partially divided by a 
septum, and is moderately expanded. 

The mandible is well developed with a prominent angle 
(fig. 72, 26), and a large coronoid process. The hyoid consists 
of a broad basi-hyal, a long many-jointed anterior cornu and 
short thyro-hyals (fig. 72, 33). 

The skull in the CREODOXTA is in most respects allied to 
that of the Canidae, but presents some ursine affinities. The 
tympanic bulla is fairly prominent^ but has no well-developed 
septum. The cranial cavity is very small and narrow, the 



480 THE VERTEBRATE SKELETON. 

zygomatic arch standing away from it. The temporal fossa is 
of great size. 

In the PISSIPEDIA the cranial cavity is large and rounded. 
The skull is much compressed in the interorbital region, and 
in correlation with this compression the ethmo-turbinals are 
little developed, while the maxillo-turbinals are large. The 
orbit is large, and the temporal fossa smaller than in the 
Garni vora vera. In the Walrus (Trichechus) the anterior part 
of the face is distorted by the development of the huge canines. 
The Otariidae have an alisphenoid canal. The tympanic bulla 
is small in Otaria, large in the Phocidae, and flattened in the 
Walrus. The hyoid is similar to that in Carnivora vera. 

INSECT: VORA. The skull varies much in the different mem- 
bers of the order Insectivora, but the following points of 
agreement are found. The cranial cavity is of small size, and 
is never much elevated. The facial part of the skull is generally 
considerably elongated, and the nasals and premaxillae are 
well developed. The zygomatic arch is usually slender or 
incomplete, and the coronoid process and angle of the mandible 
are commonly prominent. 

In some Insectivora, such as Galeopithecus, Tupaia, and 
Macroscelides, the skull shows a higher type of structure 
than is met with in most members of the order. In these 
genera the cranial cavity is comparatively large, and the 
occipital plane is nearly vertical. The zygomatic arch is fairly 
strong, and the frontal and jugal give rise to postorbital pro- 
cesses which nearly or quite (Tupaici) meet. The tympanic 
bulla is well developed, and produced into a tubular auditory 
meatus, this being specially well marked in Macroscelides. 

In the other Insectivora the cranial cavity is of smaller 
comparative size, and the orbit and temporal fossa are com- 
pletely confluent, often without any trace of a postorbital 
bar. The occipital plane commonly slopes forwards. In 
the Hedgehogs (Erinaceidae) and Centetidae the tympanic is 
very slightly developed, forming a small ring. The zygomatic 



THE SKELETON IX MAMMALIA. THE SKULL. 481 

arch of Hedgehogs and Gymnura is very slender, the jugal 
being but little developed and the squamosal and maxilla 
meeting one another ; in the Centetidae the jugal is absent 
and the arch is incomplete. 

The Moles (Talpidae) have an elongated, depressed and 
rounded skull with a very slender zygoniatic arch formed bv 
the squamosal and maxilla. The nasals are fused together, 
and the mesethmoid is ossified very far forwards. In the 
Shrews (Soricidae) there is no zygomatic arch : the tympanic 
is ring-like, and the angle of the mandible is very prominent. 
The hyoid has a transversely extended basi-hyal, a long 
anterior cornu with three ossifications, and thyro-hyals which 
metimes fused to the basi-hyal. 

CHIROPTERA. In the frugivorous Flying Foxes (Ptero- 
pidae) the skull is elongated, and the cranial cavity is large 
and arched, though considerably contracted in front. There 
are commonly strong sagittal and supra-orbital crests. The 
parietals take a great part in the formation of the walls of 
the cranial cavity, the supra-occipital and frontals being small. 
The frontal is drawn out into a long postorbital process, but 
the zygomatic arch, which is slender, and formed mainly by 
the squamosal and maxilla, gives rise to only a small post- 
orbital process, so that the orbit and temporal fossa are con- 
fluent. There is no alisphenoid canal, and the tym panics are 
very slightly connected with the rest of the skull. The man- 
dible has a large coronoid process, a rounded angle, and a trans- 
versely expanded condyle. 

In Insectivorous Bats the skull is generally shorter and 
broader than in the Pteropidae. The cranial cavity is large 
and rounded, and has thin smooth walls. The zygomatic 
arch is slender, and postorbital processes are not generally 
well developed. The premaxilla is generally small, sometimes 
absent. The tympanics are ring-like and are not connected with 
the surrounding bones. The angle of the mandible is distinct. 
The hyoid in most respects resembles that of the Insectivora, 

R. 31 



482 THE VERTEBRATE SKELETON. 

PRIMATES. The characters of the skull differ greatly in 
the two suborders of Primates, the Anthropoidea and the 
Lemuroidea. 

In the LEMUROIDEA the general relative proportions of the 
cranium and face are much as in most lower mammals, and the 
occipital plane forms nearly a right angle with the basicranial 
axis. The postorbital processes of the frontals are commonly 
continued as a pair of ridges crossing the roof of the cranium 
and meeting the occipital crest. Though the postorbital bar 
is complete, the orbit and temporal fossa communicate freely 
below it. The lachrymal canal opens outside the orbit, and the 
lachrymal forms a considerable part of the side of the face. 
The tympanic is developed into a large bulla. The hyoid 
apparatus much resembles that of the Dog. 

In the ANTHROPOIDEA the skull difi'ers greatly from that in 
the Lemuroidea. The cranial portion of the skull is very 
large as compared with the facial portion, though the 
comparative development varies, some monkeys, such as the 
baboons (Cynocephali) having the facial portion relatively large. 
The comparative size of the jaws does not vary inversely with 
the general development of the animal, some of the Cerco- 
pithecidae having comparatively larger jaws than some of the 
Cebidae. The great size of the cranial part of the skull is 
mainly due to the immense development of the cerebral fossa, 
which commonly completely overlaps the olfactory fossa in 
front, and the cerebellar fossa behind. This development also 
has the effect of making the ethmoidal and occipital planes lie, 
not at right angles to the basicranial axis, but almost in the 
same straight line with it. This is, however, not always the 
case, as the Howling Monkey (Mycetes) and also some of the 
very highest monkeys, the Gibbons (Hylobates), have the occi- 
pital plane nearly vertical to the basicranial axis. In adult 
Man the basi-occipital, exoccipitals and supra-occipital coalesce> 
forming the so-called occipital bone ; while the basisphenoid, 
presphenoid, alisphenoids, orbitosphenoids and pterygoids form 



THE SKELETON IN MAMMALIA. THE SKULL. 483 

the sphenoid bone. The roof of the skull is partly formed 
by the large supra-occipital and frontals, but mainly by the 
parietals (tig. 99, 1), which in Man are of enormous extent. 

In Man and in most monkeys, at any rate when young 
(fig. 99, B), the roof of the skull is smooth and rounded, but 
in many forms, such as the Baboons, in the adult the supra- 
orbital and occipital ridges are much developed. In the Gorilla 
this is also the case with the sagittal crest (fig. 99, A, 2). The 




FIG. 99. HALF FRONT VIEW OF THE SKULLS, A OF AS OLD, B or A. 
YOCXG GORILLA (Gorilla saragei) x%. (Camb. Mas.) 

1. parietal. 5. squamosal. 

2. sagittal crest. 6. maxilla. 

3. frontal. 7. external auditory meatus. 

4. supra-orbital ridge. 

bones of the upper surface of the cranium interlock with wavy 
outlines. The nasals vary much in length, being much shorter 
in man than in most monkeys ; they commonly become early 
fused together, as do also the frontals. The vomer is well 
developed, and the ethmo-turbinal always forms part of the 
boundary of the orbit. There are frequently, as in many 
Lemuroidea, a pair of more or less well-marked ridges, cross- 
ing the roof of the skull from the postorbital processes of the 

312 



484 THE VERTEBRATE SKELETON. 

f rentals to the occipital crest. The orbit is completely encircled 
by bone, and the alisphenoid assists the jugal and frontal in 
shutting it off from the temporal fossa, leaving however a 
communication between the two as the sphenomaxillary fissure. 
In most cases the frontals meet one another in the middle line 
between the mesethmoid and orbitosphenoid, but in Man, Simia, 
and some Cebidae this does not take place. In nearly all 
Cebidae the parietal and jugal meet one another, separating 
the frontal and alisphenoid on the skull wall ; in Man and all 
Old World monkeys, on the other hand, the alisphenoid and 
frontal meet and separate the jugal and parietal. The pre- 
maxillae nearly always send back processes which meet the 
nasals. The palate is rather short and both the palatine and 
the premaxilla take a considerable part in its formation. The 
pterygoid plate of the alisphenoid is decidedly large, and there 
is no alisphenoid canal. There is never any great develop- 
ment either of the paroccipital process of the exoccipital, or 
of the postglenoid process of the squamosal. The periotic 
and tympanic are always fused together ; in Cebidae they 
form a small bulla, but a bulla is not developed in any Old 
"World forms. The periotic is large, especially the mastoid 
portion, which forms a distinct portion of the skull wall be- 
tween the squamosal and exoccipital. In Man and still more 
in Old World monkeys, the external auditory meatus is drawn 
out into a definite tube, whose lower wall is formed by the 
tympanic ; in the Cebidae the tympanic is ring-like. The 
perforation of the periotic by the carotid canal is always 
conspicuous. 

The mandible is rather short and broad, and the angle 
formed by the meeting of the two rami is more obtuse than in 
most mammals. The coronoid process is fairly well developed, 
and the angle is more or less rounded. In most Primates tin- 
condyle is considerably widened, but this is not the case in 
Man. In Mycetes the mandible is very large, its ascending 
portions being specially developed. The hyoid of Primates is 



THE SKELETON IN MAMMALIA. AUDITORY OSSICLES. 485 

remarkable for the large expanded basi-hyal, which is generally 
concave above and convex below. The anterior cornu is never 
well ossified, but the thyro-hyal is always strong. In Mycetes 
the basi-hyal is enormously large, forming a somewhat globular 
thin-walled capsule. 

AUDITORY OSSICLES. 

There are in mammals four auditory ossicles forming a 
chain extending from the fenestra ovalis to the tympanic 
membrane. Three of these, the malleus, incus and stapes, 
are always distinct, while the fourth, the lenticular, is smaller 




s 

FIG. 100. MALLFDS, STAPES AND INCUS OF 
A. MAN. B. DOG. C. RABBIT. (After DORAN) x 1. 

1. head of malleus. 5. manubrium of malleus. 

2. canal of stapes. 6. processus brevis. 

3. incus. 7. lamella. 

4. processus longus (or gracilis). 

than the others and is sometimes not distinct. The names are 
derived from human anatomy and indicate in the case of the 
first three a more or less fanciful resemblance respectively to a 
hammer, an anvil, and a stirrup. The ossicles are homologous 



486 THE VERTEBRATE SKELETON. 

as a whole to the hyomandibular of fishes and to the columellar 
chain of Sauropsids and Amphibians. The malleus is homo- 
logous to the extracolumella of Crocodiles and the stapes 
to the columella. The malleus when typically developed 
consists of a rounded head (fig. 100, 1) which bears a surface 
articulating with the incus, and a short neck continued into a 
process, the manubrium (tig. 100, 5), which comes into relation 
with the tympanic membrane. From the junction of the neck 
and manubrium two processes are given off, a processus longus 
or gracilis (fig. 100, 4), which in the embryo is continuous 
with Meckel's cartilage, and a processus brevis (fig. 100, 6). 
The incus generally consists of a more or less anvil-shaped 
portion which articulates with the malleus, and of a process 
which is connected with the stapes by the small lenticular. 
The stapes is generally stirrup shaped, consisting of a basal 
portion from which arise two crura separated by a space the 
canal through which a branch of the pharyngeal artery runs 
The lenticular is frequently cartilaginous and sometimes is 
not developed at all. 

The above is the arrangement of the auditory ossicles met 
with in the higher Mammalia, but in the lower Mammalia 
the characters approach more nearly to those met with in 
Sauropsids. 

In MONOTRBMES the ossicles, though distinctly mammalian 
in character, show a very low type of development. The incus 
is articulated, or often fused, with an outgrowth from the 
head of the malleus. The stapes is very much like a reptilian 
columella, having a single crus with no perforation. 

In MARSUPIALS the ossicles are of a low type, but not so 
low as the rest of the skeleton might have led one to expect, 
and all or almost all the points showing a low grade of de- 
velopment may be paralleled among the Monodelphia. The 
lowest Marsupials as regards the ossicles are the Peramelidae, 
whose ossicles are of a frail papery consistence. The Didel- 
phyidae on the other hand have the most highly developed 



THE SKELETON IX MAMMALIA. AUDITORY OSSICLES. 487 

ossicles, the malleus much resembling that of many Insectivores, 
and the stapes having two definite crura separated by a canal. 

In EDENTATES the character of the ossicles varies much. 
In Sloths the stapes approaches that of Sauropsids in its 
narrowness and the slight trace of a canal : this character 
is however still more marked in Jfanis, whose stapes is as 
Sauropsidan as that of Monotremes, and consists of a nearly 
circular basal plate bearing a column which does not show any 
sign of division into crura. The stapes of other Edentates, 
such as anteaters, aard varks, and most armadillos, is of a high 
type and has well-developed crura. Priodon has a lower type 
of stapes than Dasypus and Tatusia. 

The ossicles of the SIRENIA differ widely from those of all 
other mammals in their great density and clumsy form. 

In CETACEA the ossicles are solid, though not so solid as in 
Sirenia, and their details vary much. The malleus is always 
firmly fused to the tympanic by means of the processus longus, 
and the manubrium is very little if at all developed. The 
incus has the stapedial end greatly developed, and the stapes 
has very thick crura with hardly any canal. The ossicles of 
the Mystacoceti are apparently less specialised than are those 
of the Odontoceti. 

The auditory ossicles of the UNGULATA do not present any 
characters common to all the members of the group. 

Among Ruminants they are chiefly remarkable for the 
development of a broad lamellar expansion between the head 
and the processus longus of the malleus. In some cases the 
malleus of the foetus differs strikingly from that of the adult. 
Among Perissodactyla the Rhinoceros and Tapir have the 
malleus of a low type, recalling those of Marsupials : while in 
the Horse the head is well developed, and the malleus is of 
a higher type. 

The ossicles of Procavia, which recall those of the Equiclae, 
are chiefly remarkable for the small size of the body of the 
incus. In Elephants the ossicles are large and massive. 



488 THE VERTEBRATE SKELETON. 

In the RODENTIA (fig. 100, C) the malleus is generally 
characterised by a very broad manubrium. In many genera 
such as Bathyergus, and most of the Hystricomorpha such as 
Hystrix, Chinchilla and Dasyprocta, the malleus and incus are 
ankylosed together. 

CABNIVORA. In Carnivora vera the most striking feature 
of the malleus is the occurrence of a broad lamellar expan- 
sion between the head and neck and the processus longus. 
This however does not occur in some Viverridae. In the 
Carnivora vera the incus and stapes are small as compared 
with the malleus, but in the Pinnipedia they are large. In 
the Pinnipedia the auditory ossicles have a very dense 
consistence, and except in the Otariidae are very large. The 
stapes frequently has no canal, or only a very small one. 

In INSECTIVORA the characters of the auditory ossicles are 
very diverse. Many forms such as shrews, moles, hedgehogs, 
and the Centetidae have a low type of malleus resembling that 
of Edentates. Chrysochloris has very extraordinary auditory 
ossicles. The head of the malleus is drawn out into a great 
club-shaped process, the incus is long and narrow, and differs 
much from the ordinary type. 

In CHIROPTERA the ossicles and especially the malleus much 
resemble those of shrews. The stapes is always normal in 
character, never becoming at all columelliform. 

PRIMATES. In Man and the Anthropoid Apes the malleus 
has a, rounded head, a short neck, and the manubrium, a 
processus longus and a processus brevis. The incus consists of 
an anvil-shaped portion from which arises a long tapering 
process. The stapes has diverging crura and consequently a 
wide canal. The crura in other monkeys do not diverge so 
much as in man and anthropoid apes. The New World monkeys 
have no neck to the malleus. 



THE SKELETON IN MAMMALIA. THE STERNUM. 489 



THE STERNUM'. 

In MOXOTREMES and most MARSUPIALS the sternum does 
not present any characters of special importance. The pre- 
sternum is strongly keeled in Notoryctes. 

The sternum in EDENTATES is very variable : in the Sloths 
it is very long, the mesosternum of Choloepus having twelve 
segments. In the anteaters and armadillos the presternum 
is broad and sometimes as in Priodon strongly keeled. In 
Manis macrura the xiphisternum is drawn out into a pair of 
cartilaginous processes about nine inches long. 

In the SIRENIA the sternum is simple and elongated, and 
of fairly equal width throughout, in the adult it shows no sign 
of segmentation. Its origin from the union of two lateral 
portions can be well seen in Manatus. 

Two distinct types of sternum are met with in the CETACEA. 
In the Odontoceti the sternum consists of a broad presternum 
followed by three or four mesosternal segments, but with no 
xiphisternum. Indications of the original median fissure can 
be traced, and are very evident in Hyperoodon. In the 
Mystacoceti, on the other hand, the sternum consists simply 
of a broad flattened presternum which is sometimes more or 
less heart-shaped, sometimes cross-shaped. Only a single pair 
of ribs are united to it. 

The sternum in UXGULATA is generally long and narrow and 
formed of six or generally seven segments. The presternum 
is as a rule small and compressed, often much keeled, especially 
in the horse and tapir. The segments of the mesosternum 
gradually widen as followed back and the xiphisternum is 
often terminated by a cartilaginous plate. 

In the RODENTIA the sternum is long and narrow and 
generally has a large presternum, and a xiphisternum termi- 
nated by a broad cartilaginous plate. 

1 See W. K. Parker, Monograph of the shoulder-girdle and sternum 
of the Vertebrata, Ray Soc. 1868. 



490 THE VERTEBRATE SKELETON. 

In the CARNIVORA, too, the sternum (fig. 76) is long and 
narrow and formed of eight or nine pieces, all of nearly the 
same size. The xiphisternum generally ends in an expanded 
plate of cartilage. 

In INSECTIVORA the sternum is well developed but variable. 
The presternum is commonly large and is sometimes as in the 
Hedgehog (Erinaceus) bilobed in front, sometimes as in the 
Shrew (Sorex) trilobed. It is especially large in the Mole 
(Talpa) and is expanded laterally and keeled below. 

In the CHIROPTERA the presternum is strongly keeled and 
so is sometimes the rnesosternum. 

Among PRIMATES, in Man and the Anthropoid Apes the 
sternum is rather broad and flattened ; the mesosternum 
consists of four segments which are commonly fused together 
and the xiphisternum is imperfectly ossified. 

THE RIBS. 

Free ribs are borne as a rule only by the thoracic ver- 
tebrae ; ribs may be found in other regions, especially the 
cervical and sacral, but these are almost always ankylosed to 
the verteb'rae. As a general rule the first thoracic rib 
joins the presternum, while the succeeding ones are attached 
between the several segments of the mesosternum. Some 
of the posterior ribs frequently do not reach the sternum; 
they may then be attached by fibrous tissue to the ribs in 
front, or may end freely (floating ribs). There are generally 
thirteen pairs of ribs, and in no case do they have uncinate 
processes. 

In MONOTREMES (fig. 102, B) each rib is divided not into 
two but into three parts, an intermediate portion being inter- 
posed between the vertebral and sternal parts. The sternal 
ribs are well ossified, and some are very broad and flat. The 
intermediate portions are unossified, those of the anterior ri'^ 
are short and narrow, but they become longer and wider 
further back. 



THE SKELETON IN MAMMALIA. THE RIBS. 491 

In MARSUPIALS there are almost always thirteen pairs 
of ribs, whose sternal portions are very imperfectly ossified. 
Notoryctes has fourteen pairs of ribs, eight of which are float- 
ing: the first rib is very stout, and is abruptly bent on itself 
to join the sternum. It has no distinct sternal portion. All 
the other ribs are slender. 

Of the EDENTATES the Sloths have very numerous ribs : 
twenty-four pairs occur in Ckoloepus, and half of these reach 
the sternum. In the Armadillos there are only ten or twelve 
pairs of ribs, but the sternal portions are very strongly ossified. 
The first rib is remarkably broad and flat, and is not divisible 
into vertebral and sternal portions. 

In the SIRENIA there are a very large number of ribs 
noticeable for their great thickness and solidity, but not 
more than three are attached to the sternum. 

CETACEA. In the Whalebone whales the ribs are remark- 
able for their very loose connection both with the vertebral 
column and with the sternum. The capitula are scarcely 
developed, and the attachment of the tubercula to the trans- 
verse processes is loose. The first rib is the only one connected 
with the sternum. In the Toothed whales the anterior ribs 
have capitula articulating with the centra, as well as tubercula 
articulating with the transverse processes ; in the posterior 
ones, however, only the tubercula remain. Seven pairs of 
well-ossified sternal ribs generally meet the sternum. In the 
Physeteridae most of the ribs are connected to the vertebrae 
by both capitula and tubercula. 

In the UXGULATA the ribs are generally broad and flattened, 
and this is especially the case in the genera Bos and Bubalus 
(fig. 101, 6). The anterior ribs are short and nearly straight, 
and sternal ribs are well developed. The Artiodactyla have 
twelve to fifteen pairs of ribs, the Perissodactyla eighteen or 
nineteen, and Procavia twenty to twenty-two. The Elephant 
has nineteen to twenty-one pairs, seven of which may be float- 
ing ribs. 



492 



THE VERTEBRATE SKELETON. 




THE SKELETON IX MAMMALIA. PECTORAL GIRDLE. 493 

FIG. 101. SKELETON OF A CAPE BUFFALO (Bubalus coffer). 
The left scapula is omitted for the sake of clearness x^. (Brit. Mas.) 

1. premaxilla. 7. femur. 

2. nasal. 8. patella. 

3. orbit. 9. tibia. 

4. neural spine of first thoracic 10. metatarsals. 

vertebra. 11. radius. 

5. scapula. 12. metacarpals. 

6. rib. 

In the RODEXTIA there are generally thirteen pairs of ribs, 
which do not present any marked peculiarities. 

The CARNIVORA have thirteen to fifteen pairs of ribs, 
whose vertebral portions are slender, nearly straight and 
subeylindrical, while their sternal portions are long and 
imperfectly ossified (fig. 76, 5). There is nothing that calls 
for special remark about the ribs, in either IXSECTIVORA or 
CHIROPTERA. 

PRIMATES. In Man and the Orang (Simia) there are ge- 
nerally twelve pairs of ribs ; in the Gorilla and Chimpanzee 
(Anthropopithecus), and Gibbons (Hylobates), there are thirteen, 
in the Cebidae twelve to fifteen, and in the Lemuroidea twelve 
to seventeen pairs. The first vertebral rib is shorter than the 
others, and the sternal ribs generally remain cartilaginous 
throughout life, though in man the first may ossify. 

APPEXDICULAR SKELETON. 

THE PECTORAL GIRDLE. 

By far the most primitive type of the pectoral or shoulder 
girdle is found in the MOXOTREMATA. The scapula (tig. 102, 
A, 1) is long and recurved, and has only two surfaces, one 
corresponding to the prescapular 1 fossa, the other to the post- 
scapular 1 and subscapular 1 fossae. The coracoid is a short bone 
attached above to the scapula and below to the presternurn ; 
it forms a large part of the glenoid cavity. In front of the 
coracoid there is a fairly large flattened epicoracoid (fig. 102, 6); 

1 See p. 405. 



494 



THE VERTEBRATE SKELETON. 



there is also a large T-shaped interclavicle (fig. 102, 4), 
which is expanded behind and rests on the presternum. The 
clavicles rest on and are firmly united to the anterior border 
of the interclavicle. This shoulder girdle differs greatly from 
that of any other mammals, and recalls that of some Lacertilia. 
In MARSUPIALS, as in all mammals except the Monotremes, 
the shoulder girdle is much reduced ; there are no epicoracoids 

A B 





FIG. 102. A, SIDE VIEW, B, DOBSAL VIEW or THE SHOULDER GIRDLE AND 

PART OF THE STERNUM OF THE SPINY ANTEATEB (Echidna aculedtd) 

x 1. (After PARKER.) 



1. scapula. 

2. suprascapula. 

3. clavicle. 

4. interclavicle. 

5. coracoid. 



6. epicoracoid. 

7. glenoid cavity. 

8. presternum. 

9. second sternal rib. 
10. second vertebral rib. 



and interclavicle, and the coracoid forms simply a small process 
on the scapula, ossifying from a centre separate from that 
giving rise to the rest of the bone. The scapula has a long 
acromion, and a clavicle is always present except in Perameles. 
Unossified remains of the precoracoids are found at either end 
of the clavicle. The scapula of Notoryctes has a very high 



THE SKELETON IX MAMMALIA. PECTORAL GIRDLE. 495 

overhanging spine, and there is a second strong ridge running 
along the proximal part of the glenoid border. 

The shoulder girdle of the EDENTATA shows some very 
curious variations. In. Orycteropus the scapula is of very 
normal form and the clavicle is well developed. In the Pan- 
golins and Anteaters the scapula is very broad and rounded ; 
there is no clavicle in the Pangolins, and generally only a 
vestigial one in Anteaters. In Armadillos, Sloths, and Mega- 
theriidae, the acromion is very long and the clavicle is well 
developed. In the Sloths, Megatherium, and Myrmecophaga, a 
connection is formed between the coracoid, which is unusually 
large, and the coracoid border of the scapula, converting the 
coraco-scapula notch into a foramen. In Bradypus the 
clavicle is very small, and is attached to the coracoid, which 
sometimes forms a distinct bone 1 . 

In the SIREXIA the scapula is somewhat narrow and curved 
backwards : the spine, acromion, and coracoid process are 
moderately developed, and there is no clavicle. 

CETACEA. In nearly all the Odontoceti the scapula is 
broad and somewhat fan-shaped ; the prescapular fossa is much 
reduced, and the acromion and coracoid process form flattened 
processes, extending forwards nearly parallel to one another. 
Some of the Mystacoceti, such as Balaenoptera, have a broad, 
fan-shaped scapula, with a long acromion and coracoid process, 
extending parallel to one another. Others, such as Bcdaeiui, 
have a higher and narrower scapula, with a smaller coracoid 
process. 

In UXGULATA the scapula is always high and rather narrow, 
and neither acromion nor coracoid process is ever much deve- 
loped. In no adult Ungulate except Typotherium is there any 
trace of a clavicle, but a vestigial clavicle has been described 
in early embryos of sheep 2 . 

UNGULATA VERA. In the Ruminantia the suprascapular 

1 See R. Lydekker, P. Z. S. 1895, p. 172. 

2 See H. Wincza, Morph. Jahr. xvi. p. 647, 1890. 



496 



THE VERTEBRATE SKELETON. 



region (fig. 103, 5) is very imperfectly ossified, and when this 
is removed the upper border of the scapula is very straight 
(fig. 101, 5). The spine is prominent, and generally has a 




FIG. 103. SKELETON OF A LLAMA (Auchenia <jlama) x 
(Brit. Mus.) 



hyoid. 

atlas vertebra, 
seventh cervical vertebra, 
scapula. 

5. imperfectly ossified supra- 
scapula. 



6. olecranon process of ulna. 

7. metacarpals. 

8. ilium. 

9. patella. 
10. calcaneum. 



fairly well-marked acromion. In Hippopotamus the acromion 
is fairly prominent, but in the other Suina, though the spine 
is prominent, the acromion is not developed. The Perisso- 
dactyla have no acromion, but while the Equidae and Hyra- 
cotherium have the scapula long and slender, with the spine 
very slightly developed, the other living Perissodactyla h;ivc 
the spine prominent and strongly bent back at about the 
middle of its length. 



THE SKELETON IX MAMMALIA. SHOULDER GIRDLE. 497 

SUBUNGULATA. Typotherium (Toxodontia) differs from all 
other known Ungulates in having well-developed clavicles ; 
its scapula has a strong backwardly-projecting process, much 
like that in Rhinoceros. 

Phenacodus (Condylarthra), has a curiously rounded 
scapula, with the coracoid and suprascapular borders passing 
imperceptibly into one another. The scapula resembles that 
of a carnivore more than does that of any existing Ungulate. 

Procavin has a triangular scapula with a prominent spine 
and no acromion ; there is a large unossified suprascapular 
'region. 

The scapula in the Proboscidea has a large rounded supra- 
scapular border and a narrow, slightly concave glenoid border. 
The spine is large, and has a prominent process projecting 
backwards from about its middle. The spine lies towards 
the front end of the scapula, so that the postscapular fossa is 
much larger than the prescapular fossa. 

In RODEXTIA the shoulder girdle is of a rather primitive 
type. The scapula is generally high and narrow, somewhat 
as in Ruminantia; it differs, however, from the Ruminant 
scapula in having a high acromion, which is often, as in the 
Hares and Rabbits, terminated by a long metacromion. The 
development of the clavicle varies, and sometimes it is alto- 
gether absent. It is frequently connected by cartilaginous 
bands or ligaments (fig. 104, 7 and 9), on the one hand with 
the scapula, and on the other with the sternum. These un- 
ossified bands are remains of the precoracoid. Epicoracoidal 
vestiges of the sternal ends of the coracoids (fig. 104, 11) are 
also often present. 

In the CARXIVORA VERA the scapula is large, and generally 
has rather rounded borders. The spine and acromion are well 
developed, and the prescapular and postscapular fossae are 
nearly equal in size. The coracoid is very small, and the 
clavicle is never completely developed, being often absent, as 
in the Bears and most of their allies. In the Seals (Phocidae) 
R. 32 



498 



THE VERTEBRATE SKELETON. 



the scapula is elongated and curved backwards, and has a very 
concave glenoid border. In the Eared Seals (Otariidae) the 
scapula is proportionally much larger and wider, the pre- 
scapular fossa being specially large, and being traversed by a 
ridge, which converges to meet the spine. 

7 




FIG. 104. DORSAL VIEW or THE STERNUM AND RIGHT HALF OF THE 
SHOULDER-GIRDLE OF Mus sylvciticus x 4. (After PARKER.) 



1. postscapular fossa. 

2. prescapular fossa. 

3. spine. 

4. suprascapular border unossi- 

fied. 

5. coracoid process. 

6. acromion. 

7. cartilaginous vestige of pre- 

coracoid at scapular end of 
clavicle. 

8. clavicle. 

9. cartilaginous vestige of pre- 



coracoid at sternal end of 
clavicle. 

10. omosternum. 

11. epicoracoid. 

12. presternum. 

13. first segment of mesosternum. 

14. xiphisternum. 

15. cartilaginous termination of 

xiphisternum. 

16. 2nd sternal rib. 

17. 1st vertebral rib. 



SKELETON IN MAMMALIA. UPPEK ARM AND FORE-ARM. 499 

In the INSECTIVORA the shoulder girdle is well developed 
and, as in Rodents, remains are met with of various parts not 
generally seen in mammals. In the Shrews the scapula is 
long and narrow, and has a well-marked spine, whose end 
bifurcates, forming the acromion and metacromion. The 
clavicle is long and slender, and is connected with the sternum 
and acromion by vestiges of the precoracoid. Considerable 
remains of the sternal end of the coracoid are also found. In 
Potamogale, however, there are no clavicles. In the Mole the 
shoulder girdle is greatly developed, and of very remarkable 
form. The scapula is high and very narrow, with the spine 
and acromion very little developed. The other shoulder girdle 
element is an irregular bone, which articulates with the 
humerus and presternum, and is connected by ligaments with 
the scapula. This bone appears to represent both the coracoid 
and the clavicle, being formed partly of cartilage bone, partly 
of membrane bone. 

In the CHIROPTERA the scapula is large and oval, and has 
a moderately high spine and a large acromion. The coracoid 
process is well developed and is often forked. The clavicles are 
also well developed, and vestiges of the precoracoid and of the 
sternal end of the coracoid are often found. 

In PRIMATES the clavicle and coracoid process are always 
well developed. In Man and the Gorilla the scapula has a 
long straight suprascapular border, a well-developed coracoid 
process and spine, and a large curved acromion. Vestiges of 
the precoracoid occur at each end of the clavicle. The shape 
of the scapula varies much in the lower Primates. 

THE UPPER ARM AND FORE-ARM. 

In the MONOTREMATA the humerus is short, very broad at 
each end and contracted in the middle. The radius and ulna 
are stout and of nearly equal size, while the ulna has a greatlv 
expanded olecranon. 

In the MARSUPIALIA the humerus is generally a strong bone, 

322 



500 



THE VERTEBRATE SKELETON. 



broad at the distal end and having well marked deltoid and 
supinator ridges, which are specially large in Notoryctes. An 




FIG. 105. 



ANTERIOR SURFACE OF THE RIGHT HUMERUS OF A WOMBAT 

(Phascolomys latifrons). (After OWEN.) 

6. supinator ridge. 

7. external condyle. 

8. internal condyle. 

9. articular surface for radius. 
10. articular surface for ulna. 



1. head. 

2. greater tuberosity. 

3. lesser tuberosity. 

4. deltoid ridge. 

5. ent-epicondylar (supracondy- 

lar) foramen. 



ent-epicondylar or supracondylar foramen (fig. 105, 5) is almost 
always present except in Notoryctes. The radius aud ulna are 
always distinct and well developed, and a certain amount of 
rotation can take place between them. The ulna of Notoryctes 
has an enormous hooked olecranon which causes the bone to 
be nearly twice as long as the radius. 

EDENTATA. The Sloths have long slender arm bones ; the 
humerus is nearly smooth and has a very large ent-epicondylar 
foramen in Choloepus, but not in Bradypus. The radius 



SKELETON IN MAMMALIA. UPPER ARM AND FORE-ARM. 501 

and ulna can be rotated on one another to a considerable 
extent. The humerus in all other Edentates is very strong and 
has the points for the attachment of muscles much developed, 
especially in the Armadillos and Megatheriidae. An ent- 
epicondylar foramen is found in all living forms. The radius 
and ulna are well developed, but are not capable of much 
rotation. 

In the SIRENIA the humerus is well developed and of a 
normal character. It is expanded at each end and has a 
prominent internal condyle, a small olecranon fossa, and no 
ent-epicondylar foramen. In the Dugong and Rhytina there 
is a bicipital groove and the tuberosities are distinct, but in 
the Manatee there is no bicipital groove, and the tuberosi- 
ties coalesce. The radius and ulna are about equally developed 
and ankylosed together at both ends. 

In the CETACEA the arm bones are very short and thick. 
The humerus has a globular head, and a distal end terminated 
by two equal flattened surfaces to which the radius and ulna 
are united. There is no bicipital groove, and the tuber- 
osities coalesce. The radius and ulna are flat expanded bones 
fixed parallel to one another, but the ulna has a definite ole- 
cranon. Scarcely any movement can take place between 
them and the humerus, and in old animals the three bones are 
often ankylosed together. 

In the UNGULATA VERA the humerus is stout and rather 
short. The great tuberosity is always large and often overhangs 
the bicipital groove, it is especially large in Titanotherium 
(Broniops). There is never an ent-epicondylar foramen. The 
radius is always large at both ends, but the condition of the 
ulna is very variable. Sometimes, as in Tapirus, Rhinoceros, 
Macrauchenia, Suina and Traguliiia, the ulna is well developed, 
and quite distinct from the radius ; but in most forms, although 
complete, it is much reduced distally, and is fused to the 
radius. Sometimes, as in the Horse and Giraffe, it is reduced 
to the olecranon and to a very slender descending process 



502 THE VERTEBRATE SKELETON. 

which does not nearly reach the carpus. In the Tylopoda, 
though the ulna is complete and its distal end is often distinct, 
it has coalesced with the radius throughout its whole length ; 
the olecranon is generally very large. 

SUBUNGULATA. In the large Condylarthra the humerus 
has an ent-epicondylar foramen, and the radius and ulna are 
stout bones nearly equal in size. 

In Procavia the humerus is rather long, and has a very 
prominent greater tuberosity, and a large supratrochlear fossa, 
but no ent-epicondylar foramen. 

In the Proboscidea the humerus is marked by a greatly 
developed supinator ridge, and is very long, longer than the 
radius and ulna. The ulna has a remarkable development, 
having its distal end larger than that of the radius, it has 
also a larger articular surface for the humerus than has the 
radius. 

In RODENTIA the humerus varies much in its development 
according to the animal's mode of life. In the Hares it is long 
and straight, with a small distal end, and a slight deltoid ridge. 
In the Beaver on the other hand the deltoid and supinator 
ridges are considerably developed. There is generally a large 
supratrochlear fossa, but no ent-epicondylar foramen. 

CARNIVORA. In the Camivora vera the humerus has large 
tuberosities, a prominent deltoid ridge and a deep olecranon 
fossa. The shaft is generally curved, and an ent-epicondylar 
foramen is often found, though not in the Canidae, Hyaenidae, 
and Ursidae. The radius and ulna are never united. The 
radius (fig. 77, B) has a very similar development throughout 
its whole length, while the ulna has a large olecranon (fig. 
77, C, 11) and a shaft tapering somewhat towards the distal 
end. 

In the Pinnipedia the arm bones are very strongly de- 
veloped. The humerus has a very prominent deltoid ridge, 
and the proximal end of the ulna and distal end of the 
radius are much expanded. 



THE SKELETON IN MAMMALIA. THE MANUS. 503 

In the INSECTIVORA the arm bones are well developed, and 
the radius and ulna, though sometimes united, are generally 
distinct ; as a rule there is an ent-epicondylar foramen, but this 
is absent in the Hedgehog. The Mole has an extraordinary 
humerus, very short and curved, and much flattened and ex- 
panded at both ends. It articulates both with the scapula 
and coraco-clavicle. The ulna has a greatly developed ole- 
cranon. 

In the CHIROPTERA both humerus and radius are exceed- 
ingly long and slender ; the ulna is reduced to little more than 
the proximal end and is fused to the radius. There is no ent- 
epicondylar foramen. 

All PRIMATES have the power of pronation and supinatioii 
of the fore-arm, by the rotation of the distal end of the radius 
round that of the ulua. 

In Man and the Anthropoid Apes the humerus is long and 
straight, and has a globular head ; neither of the tuberosities, 
nor the deltoid nor supinator ridges are much developed. The 
olecranon fossa is deep and there is no ent-epicondylar fora- 
men. The radius is curved and has a narrow proximal, and 
expanded distal end, the ulna is straighter than the radius 
and has the distal end much smaller than the proximal ; the 
olecranon is not much developed. 

In the lower Primates, although the radius and ulna are 
always quite separate, the power of pronation and supination 
is not nearly so great as in the higher forms. In most of the 
Cebidae and Lemurs an ent-epicondylar foramen occurs. 

THE MAXUS. 

The Manus is divisible into two parts, viz. the carpus Or 
wrist, and the hand which is composed of the metacarpals and 
phalanges. The carpal bones are always modified from their 
primitive arrangement, sometimes more, sometimes less. Or 
modification however is always found in mammals, viz. t 1 



504 THE VERTEBRATE SKELETON. 

union of carpalia, 4 and 5 to form the unciform bone. Two 
sesamoid bones are commonly developed, one on each side of 
the carpus, the pisiform or one on the ulnar side being much 
the larger and more constant : it has been suggested that 
these represent respectively vestiges of a prepollex and a post- 
minimus digit 1 . 

One or more of the five digits commonly present may be 
lost, and sometimes all are lost except the third. The terminal 
or ungual phalanges of the digits are commonly specially 
modified to support nails, claws, or hoofs. There are as a rule 
two small sesamoid bones developed on the ventral or flexor 
side of the metacarpo-phalangeal articulations, and sometimes 
similar bones occur on the dorsal or extensor side. 

MONOTREMATA. In Echidna the carpus is broad, the sca- 
phoid and lunar are united and there is no centrale. The 
pisiform is large and several other sesamoid bones occur. Each 
of the five digits is terminated by a large ungual phalanx. In 
Ornithorhynchus the man us is more slender, but the general 
arrangement is the same as in Echidna. 

MARSUPIALIA. The carpus has no centrale and the lunar 
is generally small or absent. Five digits are almost always 
present. In Choeropus however the only two functional digits 
are the second and third, which have very long closely apposed 
metacarpals ; the fourth digit is vestigial, but has the normal 
number of phalanges, while the first and fifth are absent. The 
manus in Notoryctes is extraordinarily modified, the scaphoid 
and all the distal carpalia are apparently fused, the first, 
second, and fifth digits are very small, the third and fourth, 
though having only one phalanx apiece, bear each an enormous 
claw. Lying on and obscuring the ventral surface of the manus 
is a large bone, probably a sesamoid. 

Among the EDENTATA there is a great diversity in the 
structure of the manus, the centrale is however always want- 
ing, and except in Manis the scaphoid and lunar are distinct. 

1 See K. Bardeleben, P. Z. S., 1889, p. 259. 



THE SKELETON IX MAMMALIA. THE MANUS. 505 

In the Sloths the manus is very long, narrow, and curved, 
and terminated by two or three long hooked claws, borne 
by the second and third, or the second, third and fourth 
digits. The fifth digit is absent, and the fourth is represented 
only by a small metacarpal. In the Anteaters the third digit 
is greatly developed and bears a long hooked claw. In Myr- 
mecophaga all five digits are fairly well though irregularly 
developed, in Cycloturus the first, fourth, and fifth, are vesti- 
gial. In the Armadillos the manus is broad, and has strongly 
developed ungual phalanges. The digits, though almost always 
five in number, vary much in their relative arrangement. In 
Da.iyjiiix they are regular, but are remarkably irregular in 
Prwdon. The pollex is absent in Glyptodonts and in Mega- 
thorium. In Meffatkerittat th^ fifth digit is clawless while the 
second, third, and fourth bear enormous claws. In the Manidae 
the scaphoid and lunar are united ; five digits are present, 
the third and fourth being very large, and all being terminated 
by deeply cleft ungual phalanges. In Orycteropus the pollex is 
absent, while the other digits are terminated by pointed un- 
gual phalanges. 

In SIREXIA the general structure of the manus is quite of 
the ordinary mammalian type. In Manntus most of the bones 
of the carpus are distinct, but in Halicore many, especially 
those of the distal row, have coalesced. The digits are always 
five in number and have the normal number of flattened 
phalanges. 

In the CETACEA, on the other hand, the manus is much 
modified by the fact that the number of phalanges may be 
greatly increased above the normal number of three, thirteen 
or fourteen sometimes occurring in each digit. These are 
believed to be duplicated epiphyses. In the Mystacoceti the 
manus remains largely cartilaginous, in the Odontoceti it is 
better ossified, and the phalanges commonly have epiphyses at 
both ends. In Physeter the carpal bones also have epiphyses. 
The carpus generally consists of six bones arranged in tw< 



506 THE VERTEBRATE SKELETON. 

rows of three each. Five digits are generally present, but 
sometimes as in Balaenoptera musculus, there are four, the 
third being suppressed. Their relative development varies 
much. The Sperm Whale which till recently was placed in the 
entrance hall of the Natural History Museum at South Ken- 
sington has one phalanx to the first digit, four to the second, 
five to the third, four to the fourth, and three to the fifth. 
Generally the manus is short and broad, but sometimes, as in 
Globicephalus, it is much elongated owing to the great develop- 
ment of the second and third digits. 

UNGULATA 1 . The manus of the members of this great 
order is of very great classificatory and morphological impor- 
tance. All the members agree in having the scaphoid and 
lunar distinct, and in almost every case the ends of the digits 
are either encased in hoofs or provided with broad flat nails. 
It is by means of characters derived from the manus and pes 
that the group is subdivided into the Ungulata vera and 
the Subungulata. 

In the UNGULATA VERA the manus is never plantigrade, 
and there are not more than four digits, the pollex being almost 
always completely suppressed : in Cotylops among extinct Artio- 
dactyla however a vestigial pollex is found. The centrale is 
absent, and the magnum articulates freely with the scaphoid, 
and is separated from the cuneiform by the unciform and lunar. 
All the bones of the carpus interlock strongly, and the axis of 
the third digit passes through the magnum and between the 
scaphoid and lunar. 

There is a very strong distinction between the maims of 
the suborders Artiodactyla and Perissodactyla. In the Artio- 
dactyla the axis of the manus passes between the third and 
fourth digits, which are almost equally developed and, except in 
the Hippopotami and some extinct forms such as Anoplotherium, 

1 See E. Cope, " The origin of the foot structures of Ungulata," Journ. 
of Philad. Acad. 1874. H. F. Osborn, "The evolution of the Ungulate 
foot," T. Amer. Phil. Soc. 1889. 



THE SKELETON IN MAMMALIA. THE MANUS. 507 

have their ungual phalanges flattened on their contiguous 
surfaces. 

In all ARTIODACTTLA the third and fourth digits are large, but 
a gradual reduction in the second and fifth can be well traced. 

O 

Thus in the Suina the second and fifth digits, though smaller 
than the third and fourth, are well developed and all four 
metacarpals are distinct. In the Tragulina too all four rneta- 
carpals are developed, and in Dorcatherium the third and fourth 
commonly remain distinct as in the Suina. In the other Artio- 
dactyla however the third and fourth metacarpals are almost 
always united, though indications of their separate origin 
remain. In some Ruminantia, such as many Deer, the second 
and fifth digits are reduced to minute splint bones attached 
to the proximal end of the fused third and fourth metacarpals, 
and to small hoof-bearing phalanges, sometimes attached to 
splint-like distal vestiges of the metacarpals, sometimes alto- 
gether unconnected with any other skeletal structures. In 
some other Ruminants, such as the Sheep and Oxen, the only 
remnants of the second and fifth digits are nodules of bone 
supporting the hoofs, and in others, such as the Giraffe, Ano- 
plotherium commune, some Antelopes and the Tylopoda, all 
traces of these digits have disappeared. The Camels differ 
from all living Ungulata vera in not having the distal pha- 
langes completely encased in hoofs, and from all except the 
Hippopotami in placing a considerable amount of the manus 
on the ground in walking. 

While the manus of the Artiodactyla is symmetrical about 
a line drawn between the third and fourth digits, that of the 
PEKI.^ODACTYLA is symmetrical about a line drawn through the 
middle of the third digit, which is larger than the others and 
has its ungual phalanx evenly rounded and symmetrical in 
itself. The most reduced manus in the whole of the mam- 
malia is found in the Horse and its allies, in which the third 
digit, terminated by a very wide ungual phalanx, is the only 
one functional. Small splint bones representing the second and 



508 



THE VERTEBRATE SKELETON. 



fourth metacarpals are attached to the upper part of the third 
metacarpal. In Hipparion^ and other early horse-like animals 
the second and fourth digits, though very small and function- 
less, are complete and are terminated by small hoofs. In Rhi- 
noceros the second and fourth digits are equally developed 
and nearly as large as the third, and reach the ground in 



1.. 




El 



FIG. 106. MANUS OF PEKISSODACTYLES. 

A. LEFT MANUS OF Tapirus. (After VON ZITTEL.) 

B. EIGHT MANUS OF Titanotherium. (After MAKSH.) 

C. LEFT MANUS OF Chalicotherium gigantium. (After GERVAIS.) 
scaphoid. 6. unciform. 

lunar. 7. trapezium. 



cuneiform, 
trapezoid. 
magnum. 



II, III, IV, V. second, third, 
fourth and fifth digits. 



walking, a vestige of the fifth is also present. In the Tapir 

1 See 0. C. Marsh, various papers including "Fossil horses in 
America," Amer. Natural. 1874 ; " Polydactyl horses," Atner. J. Sci. 1879 
and 1892. M. Pavlow, "Le de"veloppement des Equides," Bid. Soc. 
Moscou, 1887, and subsequent papers in the same. Osborn and Wortman, 
" On the Perissodactyls of the White River beds," Hull. Amer. Mus. Dec. 
23rd, 1895. 



THE SKELETON IX MAMMALIA. THE MANUS. 509 

(fig. 106, A) and Hyracotherium the fifth digit is fully de- 
veloped but is scarcely functional. In Titanotherium (Bron- 
tops) (fig. 106, B) it is nearly as well developed as any of the 
others, and there is little or no difference between the relative 
development of the third and fourth digits. 

The Chalicotheriidae 1 , though distinctly Perissodactyles in 
various respects such as their cervical vertebrae and teeth, 
differ not only from all other Perissodactyles, but from almost 
all other Ungulates, in the very abnormal character of their 
manus. For while the carpus and metacarpus are like those 
of ordinary Perissodactyles, the phalanges resemble those of 
Edentates, each second phalanx having a strongly developed 
trochlea, and each distal one being curved, pointed and deeply 
cleft at its termination (fig. 106, C). 

The Macraucheniidae, while agreeing with Perissodactyles 
in having only three digits, with the limb symmetrical about 
a line drawn through the middle of the third, have a carpus 
which approaches closely to the subungulate condition, the 
magnum articulating regularly with the lunar, and only to a 
slight extent with the scaphoid. 

In the SUBCXGULATA the manus sometimes has five func- 
tional digits, and a considerable part of it rests on the ground 
in walking. The bones of the carpus retain their primitive 
relation to one another, the magnum articulating with the 
lunar, but not with the scaphoid. This character does not 
however hold in the Toxodontia, for in most of the animals 
belonging to this group the magnum does articulate with the 
scaphoid. The corner of the scaphoid just reaches the magnum 
also in Amblypoda. 

As far as is known the TOSODOSTIA generally have three, 
sometimes five digits to the manus, and the third is symme- 
trical in itself a Perissodactyloid feature. 

In Phenacodus (fig. 107, B) ('OSDYLARTHRA) all five digits 

1 See H. F. Osborn, Cltalicotherium and Macrotherium, Amer. Natural. 
188991-92. 



510 



THE VERTEBRATE SKELETON. 



are well developed, the pollex being the smallest. The carpal 
bones retain their primitive arrangement, the magnum articu- 



1 ? 



1 2 3 




FIG. 107. LEFT MANUS OF 

.4. Coryphodon hamatus. (After MAKSH.) xi. 

B. Phenacodus primaevus. (After COPE.) x. 

C. Procavia (Dendrohyrax) arboreus. (After VON ZITTEL.) x f . 



1. scaphoid. 

2. lunar. 

3. cuneiform. 

4. trapezium. 

5. trapezoid. 

6. magnum. 



7. unciform. 

8. centrale. 

9. pisiform. 

I, II, III, IV, V. first, second, 
third, fourth and fifth 
digits respectively. 



lating with the lunar and not with the scaphoid. There is no 
separate centrale. 

In the HYRACOIDEA (fig. 107, C) the manus is very similar 
to that in Phenacodus, but a centrale is present and the pollex 
is much reduced. 

The manus of the AMBLYPODA, such as Coryphodon (fig. 
107, A) and Uintatherium, is short and broad, with five well- 



THE SKELETON IN MAMMALIA. THE MANUS. 511 

developed digits and large carpal bones. The carpals however 
interlock to a slight extent, and the corner of the magnum 
reaches the scaphoid. 

In the PROBOSCIDEA the manus is very short and broad, with 
large somewhat cubical carpals which articulate by very flat 
surfaces and do not interlock at all. All five digits are present, 
and none of them are much reduced in size. The manus in 
Proboscidea and in Coryphodon is subplantigrade. 

In the Tillodontia the manus is plantigrade and has pointed 
ungual phalanges, in this respect approaching the Carnivora. 
It differs however from that of all living Carnivora in having 
the scaphoid and lunar distinct. 

In RODEXTIA the manus nearly always has five digits with 
the normal number of phalanges : the pollex may however be 
very small as in the Rabbit, or absent as sometimes in the 
Capybara. The scaphoid and lunar are generally united, and 
a centrale may be present or absent. In Pedetes coffer the 
radial sesamoid is double and the distal bone bears a nail-like 
horny covering. In Bathyergus the pisiform is double. It is 
upon these facts that the contention for the former existence 
of prehallux and post-minimus digits has partly been based. 

In living CARXIVORA the scaphoid, lunar and centrale are 
always united, forming a single bone. All five digits are 
present, but as a rule in Carnivora vera the pollex is small, and in 
Hyaena is represented only by a small metacarpal. Sometimes, 
as in Cats and Dogs, the manus is digitigrade, sometimes, as in 
Bears, plantigrade. The ungual phalanges are large and point- 
ed, and in forms like the Cats, whose claws are retractile, they 
can be folded back into a deep hollow on the ulnar side of the 
middle phalanx ; a small radial sesamoid is often present. 

In Pinnipedia the manus is large and flat and the digits 
are terminated by ungual phalanges which are blunt (sea lions 
and walrus), or slightly curved and pointed (seals). The pollex 
is nearly or quite as long as the second digit, and as a rule 
the digits then successively diminish in size. 



512 THE VERTEBRATE SKELETON. 

The Creodonta differ from living Carnivora in the fact that 
the scaphoid and lunar are usually separate. 

In INSECTIVORA the scaphoid and lunar are sometimes 
united, sometimes separate, and a separate centrale is usually 
present. There are generally five digits, but sometimes the 
pollex is absent. In the Mole the manus is greatly developed 
and considerably modified. It is very wide, its breadth being 
increased by the great development of the radial sesamoid 
which is very large and sickle-shaped. The ungual phalanges 
are also large and are cleft at their extremities. 

In the CHIROPTERA the manus is greatly modified for the 
purpose of flight. The pollex is short and is armed with a 
rather large curved claw, the other digits are enormously 
elongated, the elongation in the case of the Insectivorous bats 
being mainly due to the metacarpals, and in the Frugivorous 
bats to the phalanges. In the Frugivorous bats the second 
digit is clawed as well as the pollex, in other bats this claw is 
always absent, and so is often the ungual phalanx, the middle 
phalanx then tapering gradually to its termination. 

In PRIMATES as a rule the manus is moderately short and 
wide. The carpus has the scaphoid and lunar distinct, and 
generally also the centrale : sometimes however, as in Man, 
the Gorilla, Chimpanzee, and some Lemurs, the centrale has 
apparently fused with the scaphoid. There are almost always 
five well-developed digits, but in the genera Colobus and Aides 
the pollex is vestigial. 

The magnum in man is the largest bone of the carpus. The 
pisiform also is well developed, but there is no radial sesamoid. 
In Man, the Gorilla, Chimpanzee, and Orang, the carpus arti- 
culates only with the radius, in most Primates it articulates 
also with the ulna. The third digit of the Aye- Aye (Chiromys) 
is remarkable for its extreme slenderness. 

THE PELVIC GIRDLE. 

The pelvic girdle in all mammals except the Sirenia and 



THE SKELETON IN MAMMALIA. PELVIC GIRDLE. 513 

Cetacea consists of two halves, usually united with one another 
at the symphysis in the 111 id- ventral line, and connected near 
their upper ends, with the sacral vertebrae. Each half forms 
one of the innominate bones, and includes at least three separate 
elements, a dorsal bone, the ilium, and two ventral bones, the 
ischium and pubis. Very often a fourth pelvic element, the 
acetabular or cotyloid bone, occurs. 

In the MOXOTREMATA the pelvis is short and broad, and the 
pubes and ischia meet in a long symphysis. The acetabulum 
is perforated in Echidna as in birds, but not in Ornithorhynchus. 
A pair of elongated slender bones project forwards from the 
edge of the pubes near the symphysis ; these are sesamoid bones 
formed by ossifications in the tendons of the external oblique 
abdominal muscles, and are generally called marsupial bones. 

In the MARSUPIALIA the ilia are generally very simple, 
straight, and narrow, while the pubes and ischia are well de- 
veloped and meet in a long symphysis. Marsupial bones are 
nearly always prominent, but are not developed in Tkylacinus 
or Notoryctes. The ischium often has a well-marked tuberosity 
and in Kangaroos the pubis bears a prominent pectineal 
process on its anterior border close to the acetabulum. The 
pelvis in Xotori/ctes differs much from that in all other Marsu- 
pials, the ilium and ischium being ankylosed with six vertebrae 
in a manner comparable to that of many Edentates. 

In the EDENTATA the pelvis is generally well developed, but 
the symphysis is very short. In the Sloths the pelvis is rather 
weak and slender, the obturator foramina are very large and 
the ischia do not meet in a symphysis. In the Megatheriidae 
the pelvis is exceedingly wide and massive, and is firmly 
ankylosed with a number of vertebrae. In the Armadillos, 
Glyptodonts, Anteaters, and Pangolins it is much developed 
and firmly united to the vertebral column by both the ilia and 
the ischia. In Orycteropus however the ischium does not 
become united to the vertebral column, and the pubis generally 
has a strongly developed pectineal process. 

R. 33 



514 THE VERTEBRATE SKELETON. 

In the SIRENIA the pelvis is quite vestigial. In the Dugong 
it consists on each side of two slender bones, one of which 
represents the ilium and the other the ischium and pubis ; the 
two bones are placed end to end and are commonly fused 
together. The ilium is attached by ligament to the transverse 
process of one of the vertebrae. In the Manatee each half 
of the pelvis is represented by a triangular bone connected by 
ligaments with its fellow and with the vertebral column. In 
neither Manatee nor Dugong is there any trace of an aceta- 
bulum but one can be made out in Halitherium. 

In the CETACEA the pelvis is even more vestigial than in 
the Sirenia, consisting simply of a pair of small straight bones 
which probably represent the ischia, and lie parallel to and 
below the vertebral column at the point where the develop- 
ment of chevron bones commences. 

In UNGULATA VERA the pelvis is generally rather long and 
narrow. The ilium is flattened and expanded in front (fig. 
103, 8), but becomes much narrower and more cylindrical 
before reaching the acetabulum. Both pubis and ischium 
contribute to the symphysis which is often very long. The 
ischia are large and have prominent tuberosities, especially in 
Artiodactyles. In most Ruminantia there is a deep depression, 
the supra-acetabular fossa above the acetabulum, but this is 
not found in the Suina or Tylopoda. 

SUBUNGULATA. In Procavia, the pelvis is long and narrow, 
and bears resemblance to that in Artiodactyles. 

The Proboscidea have a very large pelvis set nearly at 
right angles to the vertebral column ; the ilium is very wide, 
having expanded iliac 1 and gluteal 1 surfaces, and a narrow 
sacral 1 surface. The pubes and ischia are rather small, but 
both meet their fellows in the symphysis. Uintatherium (sub- 
order Amblypoda) also has a large and vertically placed pelvis 
(fig. 108) with a much expanded ilium. The pelvis however 

1 See p. 409. 



THE SKELETON IX MAMMALIA. PELVIC GIRDLE. 515 

differs from that of the Proboscidea in the fact that the ischia 
do not meet in a ventral symphysis. 

In many RODENTIA the ilia have their gluteal, iliac, and 
sacral surfaces of nearly equal extent ; in the Hares, however, 
the gluteal and iliac surfaces are confluent. The pubes and 
ischia are always well developed and sometimes, as in the 
Hares, the acetabular bone also. In these animals the pubis 
does not take part in the formation of the acetabulum, and 
the ischium bears on its outer side a well-marked ischial 
tuberosity. 

In the GARXIVORA the pelvis is long and narrow. The 
iliac surfaces (fig. 78, A, 5) are very small and the sacral large ; 
the crest or supra-iliac border is formed by the union of the 
sacral and gluteal surfaces. The symphysis is long and includes 
part of both pubis and ischium. The ischial tuberosity (fig. 
78, A, 10) is often well marked, and sometimes as in Viverra 
the acetabular bone is distinct. In the Pinnipedia the pelvic 
symphysis is little developed, or sometimes not developed at 
all, and the obturator foramina are remarkably large. 

In some INSECTIVORA such as Galeopithecus, there is a long 
pelvic symphysis, in others such as Erinaceus and Centetes, it is 
very short, in others again such as Talpa and Sorex, there is no 
pelvic symphysis. The acetabular bone is exceptionally large 
in Talpa and Sorex. 

In CHIROPTERA the pelvis is small and narrow, and in the 
great majority of cases the two halves do not meet in a ventral 
symphysis. The pubis has a strongly developed pectineal 
process, which occasionally unites with a process from the 
ilium enclosing a large pre-acetabular foramen. 

PRIMATES. In Man and the Anthropoid Apes the pelvis is 
very large and wide, and the ilium has much expanded iliac 
and gluteal surfaces. The symphysis is rather short and formed 
by the pubis alone. The acetabulum is deep and the obturator 
foramen large, and there is frequently a well-marked ischial 
tuberosity. In the lower Anthropoidea the ilium is long and 

332 



516 



THE VERTEBRATE SKELETON 




FIG. 108. LEFT ANTERIOR AND POSTERIOR LIMB AND LIMB GIRDLE OF 
Uintatherium mirabile. The anterior limb is to the left, the posterior 
to the right x T V (From casts, Brit. Mus. ) 

1. ilium. 4. patella. 

2. head of femur. 5. fibula. 

3. great trochanter. 6. tibia. 



THE SKELETON IN MAMMALIA. THIGH AND SHIN. 517 

7. second digit of pes. 14. radius. 

8. ungual phalanx of fifth digit 15. ulna. 

of pes. 17. unciform. 

9. calcaneum. 18. cuneiform. 

10. postscapular fossa. 20. lunar. 

11. prescapular fossa. 21. first metacarpal. 

12. coracoid process. 22. fifth metacarpal. 

13. humerus. 



narrow and has a small iliac surface. The ischial tuberosities 
are large in the old world monkeys. 

THE THIGH AND SHIN. 

In the MOXOTREMATA the femur is short, rather narrow in 
the middle, and expanded at each end. The great and lesser 
trochanters are large and about equally developed, but there is 
no third trochanter. The fibula is very large and is expanded 
at its proximal end, forming a flattened plate much resembling 
an olecranon. The patella is well developed. 

In the MARSUPIALIA there is no third trochanter to the 
femur, the fibula is well developed but not the patella as a 
general rule. S'otoryctes has a femur with a prominent ridge 
extending some little way down the shaft from the great tro- 
chanter ; the tibia has a remarkably developed crest, and the 
fibula has its proximal end much expanded and perforated ; 
there is an irregularly shaped patella closely connected with 
the proximal end of the tibia. 

EDENTATA. In the Sloths the leg bones are all long and 
slender. The femur has no third trochauter, and the fibula is 
complete and nearly equal in size to the tibia. In the Mega- 
theriidae the leg Ixmes are extraordinarily massive, the cir- 
cumference of the shaft of the femur in Megatherium equalling 
or exceeding the length of the bone. There is no third tro- 
chanter in Megatherium. In most of the remaining Edentata 
the leg bones are strongly developed. The femur in the Arma- 
dillos and Aard Yarks has a strong third trochanter, and the 



518 



THE VERTEBRATE SKELETON. 



tibia and fibula are both large and are commonly ankylosed 
together at either end. The limb bones are very massive also 
in the Glyptodonts. 

SIRENIA. In no living Sirenian is there any trace of a 
hind limb, but in Halitherium a vestigial femur is found, 
which articulates with the pelvis by a definite acetabulum. 




FIG. 109. LEFT FEMUR OF AN Ox (Bos taurus) (to the left) AND OF 
A SUMATKAN RHINOCEROS (R. sunuitrensis) (to the right), x . 
(Camb. Mus.) 

1. head. 4. third trochanter. 

2. great trochanter. 5. shaft. 

3. lesser trochanter. 6. condyles. 



In the Mystacoceti among the CETACEA small nodules of 
bone or cartilage occur connected with the vestigial pelvis, 
and may represent the femur and tibia. No trace of the 
skeleton of the hind limb is known in the Odontoceti. 



THE SKELETON IN MAMMALIA. THIGH AND SHIN. 519 

In the UNGULATA VERA the femur is noticeable for the size 
of the great trochanter (fig. 109, 2) ; there is no definitely 
constricted neck separating the head from the rest of the 
bone, and the lesser trochanter (fig. 109, 3) is not very promi- 
nent. All Perissodactyles except the Chalicotheriidae show 
a strongly marked third trochanter, but this is absent in all 
known Artiodactyles. The development of the fibula in general 
corresponds to that of the ulna. In Rhinoceros, Macrauchenia, 
Tapirus and the Suina it is distinct and fairly well developed ; 
in the Tragulina on the other hand it is vestigial, being reduced 
to the proximal end only. In the Runiinantia and Tylopoda 
also, it is much reduced forming merely a small bone attached 
to the distal end of the tibia, sometimes as in the Red deer 
a slender vestige of the proximal end also is preserved quite 
detached from the distal portion ; in the Horse this proximal 
portion is all that there is found of the fibula. The progressive 
diminution of the fibula can be well seen in the series of forms 
that are regarded as the ancestors of the Horse. The patella 
of the Ungulata vera is well ossified, but fabellae 1 are not 
usually found. 

SUBUNGULATA. Of the Toxodontia, Toxodon has no third 
trochanter while Typotherium and Astrapotherium have one. 
In the Condylarthra the femur has well-marked lesser and 
third trochanters, and the fibula and patella are well developed. 
In the Hyracoidea there is a slight ridge on the femur in the 
place of the third trochanter, the fibula is complete, but is 
generally fused to the tibia at its proximal end. 

Of the Amblypoda, Coryphodon has a third trochanter, but 
Uintatherium has none; in this respect, in the vertical position 
and general appearance (fig. 108) of the limb, and in the 
articulation of the fibula with the calcaneum, the leg of 
Uintatherium closely approaches that of the Proboscidea. 

In the Proboscidea the femur is very long and straight, 

1 See p. 412. 



520 THE VERTEBRATE SKELETON. 

the development of trochanters is slight, and the fibula though 
slender is complete and articulates with the calcaneum. 

A third trochanter is found in the Tillodontia. 

In RODENTIA the femur is variable, the great trochanter is 
generally large and so sometimes is the third as in the Hares. 
In most Rodents as in the Beaver the fibula is distinct, some- 
times as in the Hares it is united distally with the tibia. The 
patella is well developed, and so too are the fabellae as a 
general rule. 

CARNIVORA. In the Carnivora vera the femur (fig. 79, A) 
is generally rather straight and slender, and has a very distinct 
head. The fibula (fig. 79, C) is always distinct and there is 
generally a considerable interval between it and the tibia. 
Fabellae (fig. 79, 7) are commonly present. 

In the Pinnipedia the femur is short, broad and flattened, 
having a prominent great trochanter. The fibula is nearly as 
large as the tibia, and the two bones are generally ankylosed 
together at their proximal ends. 

The Creodonta differ from all living Carnivores in having 
a femur with a third trochanter. 

In the INSECTIVORA a third trochanter is sometimes 
developed. The fibula is sometimes distinct, sometimes fused 
distally with the tibia, thus differing from that of a Carnivore. 

In CHIROPTERA the femur is straight, slender and rather 
short, with a small but well-developed head. The fibula may 
be well developed or quite vestigial or absent. Owing to the 
connection of the hind limb with the wing membrane the knee 
joint is directed backwards. 

In PRIMATES the femur is rather long and slender, having 
a nearly spherical head and large great trochanter. The tibia 
and fibula are always distinct and well developed. Fabellae 
are not found in the highest forms but are generally present 
in the others. 



THE SKELETON IX MAMMALIA. THE PES. 521 

THE PES. 

The skeleton of the pes is in most respects a counterpart 
of that of the manus. Just as in the manus if one digit is 
absent it is the pollex, so in the pes it is the hallux. But 
while in the manus the third digit is always well developed, 
however much the limb may be modified, in the pes any of the 
digits may be lost. In all mammals the tibiale and inter- 
medium fuse to form the astragalus, and the fourth and fifth 
tarsalia to form the ciiboid. Sesamoid bones are considerably 
developed. In almost every case the phalanges and first meta- 
tarsal have epiphyses only on their proximal ends, while the 
remaining four metatarsals have epiphyses only on their distal 
ends. 

In the MOXOTREMATA all the usual tarsal bones are distinct, 
and the five digits have the normal number of phalanges. 
Several sesamoid bones are developed, the most important one, 
found only in the male, being articulated to the tibia and bearing 
the curious horny spur. The ungual phalanges of the pes like 
those of the manus, are deeply cleft at their extremities. In 
the Echidnidae the pes is turned outwards and backwards in 
walking. 

In the MARSUPIALIA the pes is subject to great modifica- 
tions, but in every case the seven usual tarsal bones are dis- 
tinct. In the Didelphyidae the foot is broad, all five digits are 
well developed, and the hallux is opposable to the others. 
In the Dasyuridae the foot is narrow, and the hallux may be 
very small, or as in Thylacinus completely absent. In Xoto- 
ryctes the pes is much less abnormal than the manus, and 
all five digits have the usual number of phalanges. The fifth 
metatarsal has a curious projecting process, and there is a 
large sesamoid above the ballux. In the Wombats (Phascolo- 
myidae) the foot is short and broad, the digits are all distinct, 
and the hallux is divaricated from the others. 

In the remaining marsupials the second and third meta- 
carpals and digits are very slender, and are enclosed within a 



522 THE VERTEBRATE SKELETON. 

common integument. This condition is known as syndactylism, 
and its effect is to produce the appearance of one toe with two 
claws. In the Kangaroos (Macropodidae) the pes is very long 
and narrow, owing to the elongation of the metacarpals. The 
fourth digit is greatly developed, the fifth moderately so, 
while the hallux is absent, and the second and third digits 
are very small. The Peramelidae have the foot constructed 
on the same plan as in the Kangaroos, and in one genus 
Choeropus the same type of foot is carried to a greater 
extreme than even in the Kangaroos. Thus the fourth digit 
is enormously developed, the second and third are small, and 
the fifth smaller still, while the hallux is absent. In the 
Phalangers and Koalas though the second and third toes are 
very slender, the hallux is well developed and opposable. 

EDENTATA. In the Sloths the pes much resembles the 
manus, being long and narrow, but in both genera the second, 
third and fourth digits are well developed. Most of the other 
Edentates have a but little modified pes with the normal 
number of tarsal bones and the complete series of digits. In 
Cycloturus however the hallux is vestigial and it is absent 
in Glyptodonts. Megatherium has a greatly modified pes, the 
hallux - is absent, and the second digit vestigial, while the 
third is very large, having an enormous ungual phalanx. The 
calcaneum too is abnormally large. 

No trace of the pes occurs in either SIRENIA or CETACEA. 

In the UNGULATA the pes like the manus is subject to 
much variation and is of great morphological importance. 

In the UNGULATA VERA the pes is never plantigrade and 
never has more than four digits, the hallux being absent. 
The cuboid always articulates with the astragalus, and the 
tarsal bones strongly interlock. As was the case also with the 
manus, the pes is formed on two well-marked types character- 
istic respectively of the Artiodactyla and Perissodactyla. 

ARTIODACTYLA. Just as in the manus, the third and 
fourth digits are well and subequally developed ; their ungual 



THE SKELETON IN MAMMALIA. THE PES. 523 

phalanges have the contiguous sides flat, and the axis of the limb 
passes between them, and between the cuboid and navicular. 
The astragalus has both the proximal and distal surfaces 
pulley-like, and articulates with the navicular and cuboid by 
two facets of nearly equal size. The calcaneum articulates 
with the lower end of the fibula if that bone is fully developed. 

In the Suina four toes are developed, and though in the 
Peccaries the third and fourth rnetatarsals are united, they 
are all distinct in most members of the group, as are all 
the tarsal bones. In the Hippopotami the four digits are of 
approximately equal size, and the middle ones do not have 
the contiguous faces of their ungual phalanges flattened. 

In the Tragulina the cuboid, navicular, and two outer cunei- 
forms are united forming a single bone ; all four metatarsals 
are complete and the two middle ones are united. In the 
Tylopoda and Anoplotherium commune only the third and 
fourth digits are developed, their metatarsals are free distally, 
but are elsewhere united. In the Ruminantia the cuboid and 
navicular are always united and so are the second and third 
cuneiforms, while in Cervulus all four bones are united 
together. The third and fourth metatarsals in Ruminants 
are always united in the same way as are the third and fourth 
metacarpals, while the second and fifth are always wanting. 
In Deer the second and fifth digits are usually each repre- 
sented by three small phalanges, but in the Giraffe and most 
Bovidae the bones of these digits are wanting. 

In the PERISSODACTTLA the pes like the manus is symme- 
trical about a line drawn through the third digit ; this line 
when continued passes through the external cuneiform, navi- 
cular and astragalus. The astragalus has its distal portion 
abruptly truncated, and the facet by which it articulates with 
the cuboid is much smaller than that by which it articulates 
with the navicular. The calcaneum does not articulate with 
the fibula. The tarsus in JIacrauchenia like the carpus 
differs from that of other Perissodactyles and resembles that 



524 



THE VERTEBRATE SKELETON. 
,1 




FIG. 110. A. LEFT PES OF A TAPIR (Tapirus americanus). xj. 

B. RIGHT PES OF A RHINOCEROS (R. sumatrensis). x . 

C. (CAST OF) RIGHT PES OF Hipparion gracile. xf. 

D. RIGHT PES OF A HORSE (Equux 'caballus). x fa. (All Camb. Mus.) 

1. calcaneum. 5. external cuneiform. 

2. astragalus. 6. middle cuneiform. 

3. navicular. 7. internal cuneiform. 

4. cuboid. 



THE SKELETON IN MAMMALIA. THE PES. 525 

of Subungulates in having the bones arranged in lines with 
little or no interlocking. The calcaneum resembles that of 
Artiodactyles in having a small facet for articulation with the 
fibula. Tapirus (fig. 110, A), Rhinoceros (fig. 110, B) and 
Titanotherium have a short and broad foot with the usual 
tarsal bones and three well-developed digits, a number never 
exceeded by any Perissodactyle. From this tridactylate limb 
a series of stages is exhibited by various extinct forms leading 
gradually to the condition met with in the Horse (fig. 110, D) 
in which the third toe is greatly developed, while the second 
and fourth are reduced to slender metatarsals attached to the 
proximal half of the third metatarsal. 

In Chalicotherium and Agriochoerus the pes has the same 
abnormal characters as the manus, the digits being clawed and 
the ungual phalanges in Chalicotherium deeply cleft. 

In the SUBUXGULATA the pes is sometimes plantigrade and 
pentedactylate, the cuboid sometimes does not articulate with 
the astragalus, and the tarsal bones sometimes do not inter- 
lock. 

In Typotherium (TOXODOSTIA) the hallux is absent and the 
other four digits are well developed ; in Toxodon and Nesodon 
the pes is tridactylate. The tarsal bones have the regular Sub- 
ungulate arrangement, the cuboid not articulating with the 
astragalus. The calcaneum articulates with the fibula as in 
Artiodactyles. The astragalus in most forms, but not in 
Astrapotherium, resembles that of the Ungulata vera in having 
a grooved proximal surface. 

In Phenacodus (CONDTLARTHRA) the tarsus is very little 
modified, five digits are present, the first and fifth being small 
and not reaching the ground. 

In Procavia only the three middle digits are present with 
a vestige of the fifth metacarpal. 

In the AMRLYPODA the pes (fig. 108) is very short and 
broad, all five digits are functional, and at any rate in 
Coryphodon plantigrade, the hallux being the smallest. The 



526 THE VERTEBRATE SKELETON. 

astragalus is very flat, and the tarsals interlock to a slight 
extent, the cuboid articulating with both calcaneum and 
astragalus. 

The pes in the PKOBOSCIDEA much resembles that in the 
Amblypoda, but differs in that the astragalus does not arti- 
culate with the cuboid, the tarsals not interlocking at all. 

In the RODENTIA the structure of the foot is very variable. 
In Beavers the foot is very large, all five digits being well 
developed ; the fifth metatarsal articulates with the outer side 
of the fourth metatarsal, and not with the cuboid, and there 
is a large sesamoid bone on the tibial side of the tarsus. In 
the Rats, Porcupines and Squirrels, there are five digits, in the 
Hares only four, and in the Capybara and some of its allies 
only three. In the Jerboa (Dipus) a curious condition of the 
pes is met with, as it consists of three very long metatarsals 
fused together and bearing three short toes, each formed of 
three phalanges. Lophiomys differs from all other Rodents 
in having the hallux opposable. 

CARNIVORA. In the Carnivora vera the pes is regular and 
shows little deviation from the normal condition. All the 
usual tarsal bones are present, but sometimes as in the Dogs, 
Cats, and Hyaenas, the hallux is vestigial. Sometimes as in 
the Bears the pes is plantigrade, sometimes as in the Cats and 
Dogs it is digitigrade. In this respect and in the character 
of the ungual phalanges, the pes closely corresponds with 
the manus. In the Sea Otter (Latax) the foot is large and 
flattened and approaches in character that of the Pinni- 
pedia. 

In the Pinnipedia the pes differs much from that in the 
Carnivora vera. In the Seals in which the foot cannot be 
used for walking, and is habitually directed backwards, the 
first and fifth digits are much longer and stouter than any 
of the others. In the Sea Lions which can use the pes for 
walking, the digits are all of nearly the same length, and 
in the Walrus the fifth is somewhat the longest. 



THE SKELETON IN MAMMALIA. THE PES. 527 

In the IXSECTIVORA the pes is almost "always normal, and 
provided with five digits. 

In the CHIROPTERA the pes is pentedactylate, and the digits 
are terminated by long curved ungual phalanges. In some 
genera the toes have only two phalanges. The calcaneum is 
sometimes produced into a long slender process which helps 
to support the membrane between the leg and the tail. 

Among the PRIMATES Man has the simplest form of pes. 
In Man all five digits are well developed, the hallux being 
considerably the largest. Sesamoid bones occur only under 
the metatarso-phalangeal joint of the hallux. 

In the other Primates the internal cuneiform has a saddle- 
shaped articulating surface for the hallux, which is obliquely 
directed to the side of the foot and opposable to the other 
digits. Two sesamoid bones are usually developed below 
each metatarso-phalangeal joint, and one below the cuboid. 
The second digit in Lemurs, and all except the hallux in 
CItiromys have pointed ungual phalanges; in all other cases 
the ungual phalanges are flat. In some of the Lemuroidea, 
especially Tarsius, the tarsus is curiously modified by the 
elongation of the calcaneum and navicular. 



LIST OF AUTHORS REFERRED TO. 



Abbott, E. C., 112 

Amegkino, F., 351, 424 

Andrews, C. W., 299 

Balfonx, F. M., 16 

Ballowitz, E., 424 

Bardeleben, K., 504 

Bateson, W., 50, 344 

Baum, H., 374 

Baur, G., 27, 189, 190, 344, 346 

Beneden, P. J. van, 353 

Benham, W. B., 51 

Bettany, G. T., 16. 87, 154 

Boulenger, G. A., 169 

Brandt, J. F., 352 

Bridge, T. W., 123 

BriibJ, C. B., 210 

Burmeister, H., 351, 424, 

Cope, E. D., 135, 199, 204, 351. 

359, 361, 363, 368 
Credner, H., 135 
Dean, B., 63, 104 
Dobson, G. E. , 369, 370 
Earle, C., 432 
Ecker, A., 151 
Ellenberger, W., 374 
Flower, \V. H., 28, 42, 351, 420, 

422, 434 
Fritsch, A., 135 
Fiirbringer, M., 295 
Gadow, H., 40, 112, 190, 295, 343, 

350 

Gegenbaur, C., 127 
Gervais, P., 353 
Giinther, A. C. L. G., 70, 104. 
Haslam, G., 151 
flasse, C., 112, 113 
Haswell, W. A., 127 

R. 



Hertwig, 0., 169 

Hoffmann, C. K., 190, 202, 210 

Howes, G. B., 164, 451 

Hubrecht, A. A. W., 104 

Hulke, J. W., 192, 204 

Hurst, C. H., 71, 297 

Button, F. W., 299 

Huxley, T. H., 11, 13, 133, 135, 191, 

210, 295, 297, 334, 343, 351, 374, 

437 

Kirkaldy, J. W., 51 
Klein, E., 11 
Kolliker, A., 9 
Kiikenthal, W., 349, 422 
Lankester, E. Rav, 51 
Leche, W., 344. 423 
Lindsay, B., 336 

Lydekker, R., 36, 42, 190, 195, 495 
Macbride, E. W., 50 
Marsh, 0. C., 204, 209, 299, 348, 

361, 364, 365, 508 
Marshall, A. M., 71, 151 
Mastennan, A. T., 51 
Meyer, H. v., 135 
Miall, L. C., 135, 243 
Mivart, St G., 369 
Morgan, C. Lloyd, 11 
Newton, E. T., 283 
Osborn, H. F., 348, 420, 429, 508 
Owen, R., 191, 204, 210, 297, 348, 

351, 420 

Parker, T. J., 83, 96, 299 
Parker, W. K., 16, 24, 53. 87, 154, 

173, 200, 243, 465, 489 
Pavlow, M., 358, 508 
Pollard, H. B., 119 
Poulton, E. B., 422 

34 



530 LIST OF AUTHORS REFERRED TO. 

Pycraft, W. P., 297 Thomas, 0., 349, 362, 370, 422, 

Ridewood, W. G., 106, 164 424, 425 

Rose, C., 422 Tomes. C. S., 420 

Sagemehl, M., 104 Traquair, R. H., 55, 58 

Schafer, E., 11 Vogt, C., 297 

Scott, W. B., 368 Wiedersheim, R., 25, 134, 136 

Seeley, H. G., 191, 212 Wincza, H., 358, 495 

Selenka, E., 40, 295 Woodward, A. Smith, 34, 54, 58, 

Shufeldt, R., 123 62, 127, 210 

Smith, E. Noble, 11 Wortman, J. L., 508 

Stirling, E. C., 423 Wray, B. S., 303 

Swirski, G., 103 Zittel, K. A. v., 36, 205, 212 

Taeker, J., 427 



INDEX. 



Every reference is to the page : words in italics are names of genera or 
species ; figures in italics indicate that the reference relates to syste- 
matic position ; fignres in thick type refer to an illustration ; /. and 
in following page or pages; n. =note. 



Aard Vark 44, 352; femur 517; 

sacrum 452 ; teeth 425 ; see 

Orycteropus 

Aard wolf 48 ; see Proteles 
Abdominal ribs, crocodile 260 ; 

reptiles 286 

Abdominal shield, turtle 215 
Ai-anthiaa 32 ; calcification of ver- 
tebrae 114 ; pectoral fins 130 
Acanthodes 32, 64 
Acanthodii 32 ; general characters 

64 ; spines 106 
Acanthomys 47 ; spines 417 
Acanthopterygii 34 
Accipitres 41 
Acetabular bone 25, 513; dog 409 f.; 

frog 165 
Acetabulum 25 ; crocodile 266 ; 

dog 409; duck 324; frog 165; 

newt 149 ; turtle 235 
Afipenser 32, 117 ; exoskeleton 67 ; 

distribution 66 ; pectoral fins 

131 ; plates 104 ; skull 121, 122 ; 

spinal column 112 
Acipenseridae 32 
Acrodont, defined 199 ; teeth of 

reptiles 273 
Acrodus 32 teeth 109 
Acromion, dog 405 
Actiiwtrocha 30 ; organ regarded as 

double notochord 51 



Ad-digital quill, duck 303 
Adjutant 41 ; clavicles 338 
.Egithognathous 335 
.Eluroidea 48, 369 ; teeth 437 
J3pyornis 40 ; tibio-tarsus 341 
.Epyornithes 40, 299 
Aftershaft 328 
Agama 38 ; teeth 273 
Agamidae 38 ; premaxillae 284 
Aglossa 36 

Agouti 48 ; see Dagyprocta 
Agriochoeridae 46 
Agriochoerus 45 ; pes 525 
Ala spuria, duck 304 
Alcidae 42 see Auks 
Alisphenoid 19 ; crocodile 247 ; duck 

317 ; dog 386 
Alligator 39, 210, 212 ; hyoid 285 ; 

limbs 264 ; pectoral girdle 262 ; 

pelvis and sacrum 267 ; scutes 

271; skull 245. 248, 253 
Alligatoridae .39 
A lytes 36 ; fronto-parietal fontanelle 

179 ; vertebrae 172 
Amblypoda 47 ; general characters 

363 ; manus 510 ; pes 525 ; skull 

473 ; teeth 433 ; thigh and shin 

519 

Amblystoma 35; skull 175 
American monkeys 373; see Ce- 

bidae 

342 



532 



INDEX. 



American vultures 41 ; vomers 335 
Amia 33; distribution 66; exo- 

skeleton 67 ; pectoral fin 131 ; 

scales 105; skull 123; tail 115, 

117 ; vertebrae 114 
Amiidae 33 
Ammocoetes 31, 55 
Amphibia 35 ; anterior limb 185 ; 

exoskeleton 168 ; general charac- 
ters 133 ; hyoid apparatus 180 ; 

pectoral girdle 184 ; pelvic girdle 

187 ; posterior limb 188 ; ribs 

182; skull 173; sternum 182; 

teeth 169 ; vertebral column 170 
Amphicoelous, defined 14 
Amphioxus 30; skeleton 51 f. ; spinal 

column 112 
Amphisbaena 38, 272 ; loss of limbs 

289 
Amphisbaenidae 38, 200; pectoral 

girdle 288; skull 277; vertebral 

column 275 
Amphitheriidae 43 
Ainphiuma 35, 135 ; manus 187 ; pes 

188; skull 174 
Amphiumidae 35 
Anacanthini 33 
Anal shield, turtle 215 
Anas 41 ; A. boschas, see Duck 
Ankylosis, defined 12 
Angel fish 32 

Angler, attachment of teeth 107 
Anguidae 38 
Anguilla 33 ; see Eel 
Anguis 38 ; loss of limbs 289 ; scutes 

271 
Angular 22 ; cod 100 ; crocodile 

258; duck 319; salmon 94; turtle 

231 

Angulo-splenial, frog 161 
Ankle joint, duck 327 ; reptiles 294 
Anomodontia 36 
Anoplotheriidae 45 
Anoplotherium 45; manus 506; pes 

523; tail 454; teeth 428 
Anser 41 
Anseres 41 ; aftershaft 329 ; claws 

330 

Anseriformes 41 
Anteaters 352 ; absence of teeth 

424 ; manus 505 ; pectoral girdle 

495; pelvis 513; skull 458; tho- 

raco-lumbar vertebrae 447; Spiny 



43 ; Great and Two-toed 
44 

Antelope 359 ; manus 507 ; Four- 
horned A. 46 

Anterior limb 26 ; Amphibia 185 ; 
birds, 338; crocodile 263; dog 
405; duck 322; frog 164; newt 
147; reptiles 290; turtle 232 

Anthropoid apes 373; arm-bones 
503; pelvis 515 

Anthropoidea 49 ; general charac- 
ters 372; sacrum 452; skull 482; 
teeth 441 

Anthropopithecvs 49 ; ribs 493 

Antiarcha 31 ; general characters 55 

Antibrachium, see fore-arm 

Antilocapra 46 ; horns 417 

Antilocapridae 46 

Antitrochanter, duck 325 

Antlers 8, 358; Cervidae 469 

Antorbital process 18 

Anura 36 ; general characters 136 ; 
hyoid apparatus 180 ; pelvis 187 ; 
posterior limb 188; sknll 179: 
sternum 182; vertebrae 172 

Apatornis 40 ; vertebrae 332 

Apteria 328 

Apteryges 40 

Apteryx 40, 299 ; aftershaft 329 ; 
anterior nares 333 ; claws 330 ; 
foot 342 ; manus 338 ; pectineal 
process 341 ; pectoral girdle 338 ; 
pneumaticity of skeleton 331 ; A. 
oweni, pelvic girdle and sacrum 
340 

Aqueductus vestibuli, dogfish 74 

Arcade: infratemporal , crocodile 
255; Sphcnodon 283; inner , 
duck 318 ; outer , duck 318 : 
supratemporal , crocodile 257 ; 
reptiles 281 

Archaeoceti 44 ; general characters 
356 ; skull 461 ; teeth 426 

Archaeopteryx 40, 297 ; claws 330 ; 
fibula 341 ; mandible 335 ; rneta- 
tarsals 342 ; pelvis 341 ; ribs 
336 ; sacrum 333 ; skull 333 ; 
tail 333; teeth 330; wing 338 

Archaeornithes 40 ; characters 297 

Archefjosaurus 35, 136; palatines 
177 

Archipterygium, Ceratoditx 127 ; 
Ichthyotomi 62 



INDEX. 



533 



Arcifera 36, 185 

Arctoidea 48, 369 ; teeth 438 

Ardea 41 ; see Heron 

Ardeae 41 

Arm, see fore-arm and upper arm 

Armadillo 44, 352 : cervical verte- 
brae 443 ; femur 517 ; hnmerus 
501 ; lumbar vertebrae 447 ; ma- 
nus 505 , pectoral girdle 495 ; 
pelvis 513 ; ribs 491 ; sacrum 
452 ; scales 417 ; scutes 419 ; 
skull 459 ; teeth 424 

Armour plates 8 

Arthrodira 34 ; characters 70 

Articular 22 ; cod" 100 ; crocodile 
duck 319 ; newt 144 ; sal- 
mon 94 ; turtle 231 

Artiodactyla 4-5 ; characters 358 ; 
manus 506 ; odontoid process 
445 ; pes 522 ; ribs 491 ; skull 
465 ; teeth 427 ; thoraco-lumbar 
vertebrae 448 
360 

Asterolepis 31, 55 

Asterospondyli 114 

Astragalus 27 ; crocodile 268 ; dog 
414 ; mammals 521 

Astrapotheriidae 46 

Astrapotherium 46, 361; dental 
formula 432 : femur 519 ; pes 
525 

Atele* 49 ; pollex 512 ; tail 454 

Atlautosauridae 38 

Atlas 15; crocodile 240 ; dog 379, 
380 ; duck 309 ; ox 445 ; turtle 
219 

Attachment of teeth 4 ; in fish 107 

A uchenia 45 ; see Llama 

Auditory aperture or meatus : ex- 
ternal , crocodile 250 ; dog 402 ; 
turtle 2*28 ; internal , crocodile 
246, 251 ; dog 392 ; turtle 228 

Auditory capsule 20 ; cod 96 ; cro- 
codile 250 ; dog 390 ; dogfish 74; 
frog 156 ; newt 143 ; turtle 227 

Auditory ossicles, crocodile 251 ; 
dog 393 ; duck 320 ; mammals 
485 f.; turtle 228 

Auks 42 ; thoracic vertebrae 332 

Autostylic 61, 119 

Avts 40 ; characters 295 ; see Birds 

Axial skeletal rods 50 

Axial skeleton, crocodile 239 ; cod 



83 ; dog 317 ; dogfish 72 ; duck 

307 ; frog 152 ; newt 138 ; turtle 

218 
Axis vertebra, crocodile 241 ; dog 

380 ; duck 309 ; turtle 220 
Axolotl 3-5 ; see Siredon 
Aye Aye ^9; see Chiromys 



Babirussa 45 ; dental formula 428 

Baboon 49 ; see Cynocephalus 

Balanoglossus 30, 50 

Balaena 44, 357 ; scapula 495 ; 
B. mysticetus baleen 419 

Balaenidae 44 

Balaenoidea 44 ; general characters 
356 

Balaenoptera 44, 357; manus 506; 
thoracic vertebrae 448; scapula 
495 ; B. musculus, cervical verte- 
brae 444 

Baleen 3, 418 

Balistes33; teeth 111 

Balistidae 33 

Ball and socket joints 13 

Bandicoot 43 

Barb 302 

Barbule 303 

Barramunda 34 ; see Ceratodus 

Basalia, dogfish 79 

Basi-branchial, dogfish 78; cod 101; 
duck 320 ; newt 145 ; salmon 95 

Basi-branchiostegal, cod 101; sal- 
mon 95 

Basicranial axis 19 ; dog 384 

Basidorsalia, dogfish 72 

Basi-hyal, dogfish 78; dog 399; 
duck 320 

Basilar plate 17 

Basilingual plate, Anura 180 ; cro- 
codile 259 ; frog 161 ; turtle 231 

Basi-occipital 19 ; crocodile 246 ; 
cod 97; dog 386; duck 315: 
salmon 89 ; turtle 224 

Basipterygium, cod 103 ; dogfish 82 ' 

B a si sphenoid 19 ; crocodile 247 ; 
dog 386 ; salmon 91 ; turtle 225 

Bastard whig, duck 304 

Bathyerginae, palate 366 

Bathyergus 47 ; auditory ossicles 
488 ; manus 511 

Batoidei 32, 64 

Batrachoseps 35 ; teeth 169 



534 



INDEX. 



Bats, claws 418 ; Horseshoe bats 
49 ; see Ghiroptera 

Bdellostoma 31, 55 ; teeth 57 

Beak 3 ; birds 329 ; duck 302 ; 
Siren 168 ; tadpoles of Anura 
168 ; turtle 215 

Bears 48, 369 ; manus 511 ; pes 
526 ; sacral vertebrae 452 ; skull 
479 ; Isabelline mandible 438 

Beaver 47 ; fibula 520 ; humerus 
502 ; pes 526 ; sacrum 452 ; tail 
454 

Belodon 39, 211 ; frontals 277 ; 
palate 281 ; vertebrae 275 

Bichir 33 ; see Polypterus 

Bicipital groove, dog 405 

Bilophodont, defined 345 ; teeth of 
Tapiridae 429 

Bipes 38 ; limbs 289 

Birds, anterior limb 338 ; endo- 
skeleton 331 f.; exoskeleton 328 f.; 
general characters 295 ; hyoid 
336 ; pectoral girdle 336 ; pelvic 
girdle 339 ; posterior limb 341 ; 
ribs 336 ; skull 333 ; sternum 336 ; 
teeth 330 ; vertebral column 332 

Bison 46 ; occipital crest 468 

Blind snake 3<5 ; see Typhlops 

Blind worm 38 ; see Anguis 

Boidae 38 

Bombinator 36 ; vertebrae 172 

Bone, development of 10 f. 

Bone cells 10 

Bony Ganoids, fins 105 ; pelvic fin 
132 ; ribs 126 ; skull 123 ; verte- 
bral column 114 ; see Holostei 

Border: alveolar , of dog's jaw 
398 ; coracoid, glenoid, and supra- 
scapular of dog's scapula 405 

Bos 46 ; occipital crest 468 ; ribs 
491 ; see Ox 

Bottlenose 44.; see Hypero'odon 

Bovidae 46 ; pes 523 ; skull 468 

Bow-fin 33 ; see Ami a 

Brachial ossicles, cod 103 

Brachium ; see upper arm 

Brachydont, defined 345 ; teeth of 
Ungulates 429 f. 

Brachycephalus 36 ; bony plates of 
168 

Brain case, crocodile 245 ; dog .384 ; 
duck 314 ; frog 154 ; newt 140 ; 
turtle 224 



Bradypodidae 43 ; see Sloths 
Bradypm 43 ; cervical vertebrae 

443 ; pectoral girdle 495 ; skull 

457 ; thoraco-lumbar vertebrae 

447 
Branchial arches, Amphibia 180 f . : 

cod 101 ; dogfish 78 ; fish 120 f. : 

newt 145; salmon 95 ; basket, 

Marsipobrauchii 38 ; skeleton, 

Amphioxus 52 ; Balanoglossus 

50 
Branchiosatirus 35 ; branchial 

arches 180 

Branch iostegal rays, cod 100 
Brontops 46 ; see Titanotherium 
Brontosaurus 38, 207 ; sternum 288 
Bubalus 46 ; ribs 491 ; see Buffalo 
Buccal skeleton, Amphioxus 52 
Buceros 42 ; see Hornbill 
Buckler, of Labyrinthodonts 168, 

184 
Buffalo 46; Cape , skeleton of 

492 
Bufo 36 ; hyoid 182 ; jaws 169 ; 

B. viridis, carpus 186 
Bufonidae 36 
Bunodont, defined 345 ; teeth of 

Ungulata 427 f. 
Buno-selenodont, denned 432 

Caeciliidae 35 

Caiman 39; C. latirostris hyoid 
285, limbs 264, lateral view of 
skull 248, palatal view of cra- 
nium and mandible 245, longi- 
tudinal section of skull 253, 
pectoral girdle 262, pelvic girdle 
and sacrum 267 ; C. scli'rop*. 
scutes 271 

Ca'ing whale 45 ; see Globicejihlu 

Calamoichthys 33 ; distribution 66 

Calamus 302 

Calcaneum 27 ; crocodile 268 ; dog 
414 

Calcar, of frog 167 

CaUorhynchus 32, 66 ; teeth 110 

Camel 45, 359 ; manus 507 ; teeth 
428 

Camelidae 45 

Camelus 45 ; see Camel 

Camptosauridae 39 

Canal: alisphenoid , dog 402; ca- 
rotid , duck315 ; Eustachian , 



INDEX. 



535 



crocodile 247 ; dog 402 ; duck 
316 ; interorbital , dogfish 76 

Canaliculi 10 

Canidae 4S ; humerns 502 ; sknll 
479 ; see Dog 

Canine 344 ; dog 376 f. 

Cam's 48 ; thoraco-lumbar verte- 
brae 450 ; see Dog 

C<ipitosauru* 35 ; skull 176 

Capybara 48; manus 511 ; pes 526 ; 
skull 476 ; tail 454 

Carapace. Chelonia 271 ; Dermo- 
chely* 272 ; Glyptodonts 419 ; 
Green turtle 215 ; Loggerhead 
turtle 216 

Carcharidae 32 

Carina sterni, duck 321 

Carinatae 40 ; general characters 
300 ; quadrate 334 

Carnassial teeth, 368 ; camivora 
436 ; dog 376 f. 

Camivora 48 ; arm bones 502 ; 
auditory ossicles 488; cervical 
vertebrae 446 ; general characters 
367 ; manns 511 ; pelvis 515 ; 
pes 526 ; ribs 493 ; sacral verte- 
brae 452 ; skull 478 ; sternum 
490; tail 454; teeth 437; thigh 
and shin 520 ; thoraco-luinbar 
vertebrae 450 

Carnivora vera 48 ; general charac- 
ters 368 ; scapula 497 

Carp 33 ; pharyngeal teeth 111 

Carpo-metacarpus, duck 324 

Carpus 2fi ; crocodile 265 ; dog 408 ; 
duck 323 ; frog 164 ; newt 147 ; 
turtle 233 

Cartilage, structure of 10 

Cartilaginous ganoids, cranium 
121 ; pelvic fin 132 ; spinal 
column 112 ; see Chondrostei 

Cassowary 40, 299 ; aftershaft 32* : 
bony crest 334 ; claws 330 ; pel- 
vic girdle and sacrum 34O : 
secondaries 329 

Castor 47 ; see Beaver 

Castoridae 47 

Casuarius 40 ; see Cassowary 

Cataphracti 34 

Cat 48, 369 ; hallnx 526 ; manns 
511; skull 479 

Cat-fish 33 

Cathartae 41 



Cathartes 41 ; see American vulture 
Caudal fin, Getacea 453 ; fish 116 : 

vertebrae, crocodile 243 ; 

cod 85; dog 383; duck 312; 

general characters 16 ; newt 140 ; 

turtle 222 
Cacia 48 ; tail 454 
Caviidae44 
Cebidae 49, 373; ribs 493: skull 

484 ; teeth 441 
Coenoleste* 43, 424 
Cement 5 
Centetes 49 ; caudal vertebrae 454 ; 

pelvic symphysis 515 ; spines 

417 ; teeth 440 ; thoraco-lnmbar 

vertebrae 450 
Centetidae 49 ; auditory ossicles 

488 ; sknll 480 

Centrale 27 ; see Carpus and Tarsus 
Centre of motion 448 
Centrum 14 
Cephalaspis 31, 55 
Cephalic shield, armadillos 419 
Cephalochordata 30, 51 
Cephalodiscus 30, 50 
Ceratodu* 34, 70 ; branchial arches 

124 ; cranium 135 ; skeleton 

128 ; skull 117, 124 ; spinal 

column 113 ; teeth 111 
Cerato-branchial, cod 101 ; dogfish 

78 ; duck 320 ; salmon 95 
Cerato-hyal 23 ; cod 100 ; dog 399 ; 

dogfish 78 ; salmon 95 
Ceratophrys 36 ; bony plates of 

168 ; teeth 170 
Ceratops 39 ; see Polyonax 
Ceratopsia 39 ; characters 209 ; 

premaxillae 284 
Ceratopsidae 39 

Ceratosaurug 38, 208 ; supra- 
temporal fossae 283; C. nati- 

cornis, skeleton 2O6 
Cercopithecidae 49. 373 
Cervical ribs, crocodile 260 : rep- 
tiles 285 
Cervical vertebrae, crocodile 239 : 

dog 380; duck 307; general 

characters 15 ; mammals 442 : 

turtle 219 

Cervidae 46 ; skull 469 
Cerrulu* 46 ; pes 523 
Ccrrus 46; C. megacerot, antlers 

469 



536 



INDEX. 



Gestracion 32 ; calcification of 
vertebrae 114 ; external bran- 
chial arches 121 ; pectoral fin 
130; skull 118; suspensorium 
119 ; teeth 109 ; vertebral column 
114 

Cestraciontidae 32 

Cetacea 44, 522 ; arm bones 501 ; 
auditory ossicles 487 ; caudal ver- 
tebrae 453 ; cervical vertebrae 
444 ; characters 353 ; exoskeleton 
416 f. ; hind limb 518 ; manus 
505 ; pectoral girdle 495 ; pelvis 
514 ; position of limbs 28 ; ribs 
491 ; skull 461 f. ; sternum 489 ; 
teeth 426 ; thoraco-lumbar ver- 
tebrae 448 

Cetiosauridae 38 

Chalcides 38 ; limbs 289 

Chalicotheriidae 46 ; femur 519 ; 
manus 509 

Chalicotherium 46 ; femur 360 ; pes 
508, 525 ; teeth 432 

Chamaeleon 38, 199 f. ; epipubis 
293 ; ilia 291 ; mauus 291 ; skull 
278 

Chamaeleonidae 38 

Charadriidae 42 

Charadriiformes 42 

Chauna 41 ; interorbital septum 
333 ; ribs 336 ; C. derbiana, spurs 
330 

Chelone 37, 194; plastron 271, 2 18; 
see Turtle 

Chelonia 37; beaks 271; carapace 
271 ; general characters 193 ; 
humerus 290 ; limbs 290 ; palate 
281 ; pectoral girdle 288 ; pelvic 
girdle 291 ; skull 277 f. ; tarsus 
293 ; vertebrae 275 f. 

Chelonidae 37 

Chelydae 37 

Chelydra 37 ; carpus 26, 291 

Chelydridae 37 

Chelys 37, 195 

Chersidae 37 

Chevron bones 16 ; crocodile 243 ; 
mammals 453 f. ; reptiles 276 

Chevrotain 45, 359 ; teeth 429 

Chimaera 32, 66 ; attachment of 
fins 130 ; pelvic girdle 127 ; skull 
65 ; teeth 110 

Chimaeridae 32 



Chimaeroidei, general characters 65 

Chimpanzee 49 ; carpus 512 ; ribs 
493 ; thoraco-lumbar vertebrae 
450 

Chinchilla 47 ; auditory ossicles 
488 

Chinchillidae 47 

Chiromyidae 49 

Chiromys 49, 372 ; manus 512 ; pes 
527 ; teeth 441 

Chiroptera 49 ; auditory ossicles 
488 ; arm bones 503 ; cervical 
vertebrae 446 ; general characters 
370; manus 512; pelvis 515.; 
pes 527 ; sacrum 452 ; shoulder 
girdle 499 ; skull 481 ; sternum 
490 ; tail 454 ; teeth 440 ; thigh 
and shin 520 ; thoraco-lumbar 
vertebrae 450 

Chirotes 38 ; limbs 289 

Chlamydophorus 44, 272 ; scutes 
419 ; skull 459 

Chlamydoselache 31 ; branchial 
arches 121 

Choeropus 43 ; manus 504 ; pes 
522 

Choloepus 43 ; ribs 491 ; shifting of 
pelvis 451 ; skull 458 ; sternum 
489 ; thoraco-lumbar vertebrae 
447 ; C. hoffmanni cervical verte- 
brae 443 

Chondrocranium, salmon 87 

Chondroid tissue, Balanoglossus 50 

Chondrostei 32 ; fins 105 ; general 
characters 67 ; teeth 110 ; see 
Cartilaginous ganoids 

Chordal sheath, Amphioxus 52 

Chrysochloridae 49 

Chrysochloris 49 ; auditory ossicles 
488 ; claws 418 ; teeth 440 

Ciconia 41 ; see Stork 

Ciconiiformes 41 

Cingulum 376 

Civet 48, 369 ; teeth 437 

Cladoselache 31, 63 ; fin 129 

Clasper 132 ; dogfish 82 

Clavicle 25; birds 338; cod 102; 
duck 322; dog 405; fish 126; 
frog 163 ; mammals 494 f. ; rep- 
tiles 289 

Claws 3 ; birds 330 ; crocodile 237 ; 
dog 374 ; duck 302 ; mammals 
417 ; turtle 215 



INDEX. 



537 



Clupeidae 33 

Clupeus 33 

Cnemial crest, dog 412 ; duck 326 

Coccosteug 34, 70 

Coccyx, rnan 454 

Cochliodontidae 31 

Cochliodm 31 ; dental plates 109 

Cod 33 ; appendicular skeleton 
101 f. ; cranium 96 ; mandibular 
and hyoid arches 99 ; median 
fins 86 ; pectoral girdle and fin 
102; ribs 86; skull 96 f.; verte- 
bral column 83 f. 

Cfjtlmienys 48 ; zygomatic arch 
477 

Coenolestes 43, 424 

Coffer-fish 33 ; see Ostracion 

Colobm 49 ; pollex 512 

Colubridae 38 

Columbae 42 

Columbidae 42 

Columella, crocodile 251 ; duck 
320 ; frog 157 ; turtle 228 

Columella cranii, 200 n. ; see epi- 
pterygoid 

Colymbi 40 

Colymbiformes 40 

Compsognathidae 38 

Compsognathus 38, 208 

Condylar ridge, duck 326 

Condyle of humerus, dog 406 ; of 
mandible, dog 398 

Condylarthra 47 ; femur 519 ; 
general characters 361 ; manus 
509 ; skull 472 ; teeth 432 

Contour feather, duck 303 

Copula 23 

Coracias 42 ; see Roller 

Coraciae 42 

Coraciiformes 42 

Coracoid 25 ; cod 103 ; crocodile 
263 ; duck 322 ; frog 163 ; Mono- 
tremata 493 ; newt 147 ; reptiles 
288 ; turtle 232 

Coracoid groove, duck 321 

Cormorant 41 ; foot 342 ; skull 335 

Cornu, see hyoid 

Cornua trabeculae 18 

Coryplwdon 47 ; femur 519 ; manus 
510 ; pes 525 ; skull 473 ; teeth 
433 ; C. hamatu*, manus 51O 

Coryphodontidae 47 

Costal plate, turtle 215 ; process, 



duck 321; shield, turtle 
214 

Cotyloid bone, 25, 513 ; see Ace- 
tabular bone 

Cotylopidae 4-5 

Cotylops 45; pollex 506 ; skull 468 

Coverts 306, 328 

Cranium 18 ; cod 96 f. ; crocodile 
244 f. ; development of 16 f . ; dog 
384 f. ; dogfish 73 f. ; duck 314 ; 
frog 154 f. ; newt 140 f. ; turtle 
222 f. 

Cranio-facial axis, dog 384 

Creodonta 48 ; carpus 512 ; femur 
520 ; general characters 368 ; 
skull 479 ; teeth 439 

Cribriform plate, dog 388, 400 

Crocodile 210, 212; anterior limb 
263 ; exoskeleton 237 ; pectoral 
girdle 262; pelvic girdle 266; 
posterior limb 268 ; ribs and 
sternum 259 ; skeleton 237 f. ; 
skull 243 f. ; tarsus 293 ; teeth 
238 ; vacuities in surface of cra- 
nium 256 ; vertebral column 239 

Crocodilia 39 ; general characters 
of 210 ; palate 281 ; skull 277 f.; 
succession of teeth 274 ; teeth 
273 

Crocodilidae 39 

Crocodilus 39; C.pahistris,stemnm 
and associated bones 261 ; late 
thoracic and first sacral verte- 
brae 242 ; C. rulgaris, cervical 
vertebrae 239 

Crossopterygii 33 ; general charac- 
ters 68 

Crotalidae 38 

Crotalus 38 ; jaws 280 ; see Eattle- 
snake 

Crows 42 

Crura of stapes, dog 393 

Cruro-tarsal, aukle joint 345 

Crus, 26 ; crocodile 268 ; dog 412 ; 
duck 326 ; frog 166 ; newt 149 ; 
turtle 235 

Crusta petrosa 5 

Cryptobranchus 35, 135 ; skull 175 ; 
C. lateralis, sacral vertebrae 171 

Cryptodira 37 ; characters 194 

Ctenoid scales 8, 60, 105 

Cubitals 303 f. 

Cuboid 27 ; dog 415 



538 



INDEX. 



Cuckoo, foot 342 

Cuculi 42 

Cuculiformes 42 

Cuneiform bones 27 ; dog 414 f. 

Cyclodus 38 ; see Tiliqua 

Cycloid scales 8, 60, 105 ; cod 83 

Cyclopidins 45 ; skull 468 

Cyclospondyli 114 

Cyclostomata 31 ; general charae- 

' ters 53 
Cycloturus 44 ; hallux 522 ; manus 

505 

Cygniis 41 ; see Swan 
Cynocephalus 49 ; cervical vertebrae 

446 ; skull 482 
Cynoidea 48, 369 ; dental formula 

437 
Cynognathits 36 ; occipital condyle 

277 ; teeth 273 
Cyprinidae 33 
Cyprinus 33 ; see Carp 
Cypseli 42 

Cypselidae 42 ; see Swifts 
Cystignathidae 36 

Dactylopterus 34 ; pectoral fins 131 

Dasypodidae 44 

Dasyprocta 48 ; auditory ossicles 
488 ; thoraco-lumbar vertebrae 
450 

Dasyproctidae 48 

Dasypus 44 ; manus 505 ; skull 
459 ; stapes 487 ; teeth 424 

Dasyuridae 43, 350 ; dentition 423 ; 
pes 521 ; skull 456 

Deer 359 ; manus 507 ; pes 523 ; 
Chinese water 46, see Hydro- 
potes ; Musk 46, see Muschus ; 
Bed fibula 519 

Delphinidae 45 

Delphinus 45, 357 ; lumbar verte- 
brae 448 ; skull 462 f. 

Deltoid ridge, crocodile 263 ; dog 
406 ; frog 164 

Deiidrohyrax 363 

Dental formula, regular 344, 422 ; 
Anthropoidea 441 ; Astrapothe- 
rium 432 ; Balirussa 428 ; Camel 
428 ; Chiromys 441 ; Chiroptera 
(many) 440 ; Cynoidea 437 ; 
Dinotherium 434 ; Dog 376 ; Du- 
plicidentata 435 ; Elephas 434 ; 
Erinaceus 440 ; Felis 437 ; Galeo- 



pithecus 440 ; Hippopotamus 427 ; 

Horse 430 ; Hydromys 436 ; 

Hyracoidea 362; Macropodidae 

423 ; Manatus 425 ; Notoryctex 

423 ; Otaria 439 ; Procavia 432 ; 

Pteropus 441 ; llodentia (most) 

435; Euminantia 429; Sqnulo- 

don 427 ; Sns 428 ; Tapiridae 

429 ; Thylacinus 423 ; Uinta- 

therium 433 ; Ursus 439 ; Zeuy- 

lodon 426 
Dentary 22 ; crocodile 258 ; cod 

100 ;' duck 320 ; frog 161 ; newt 

144 ; salmon 94 ; turtle 230 
Dentine 5 

Derbian Screamer, spurs 330 
Dermal exoskeletou, crocodile 237 ; 

fish 105; mammals 419 ; reptiles 

271 ; turtle 215 
Dermo-supra-occipital,Labyrintho- 

dontia 177 ; Polypterus 122 
Dermochelydidae 37 
Dermochelys 37, 194, 214, 270 ; 

carapace and plastron 272 
Dermoptera 48 ; general characters 

370 

Derotremata 35 
Desmodus 49 ; teeth 441 
Desmognatbous 319, 335 
Development of bone 10 ; of 

cranium 16 ; of teeth 7 
Dicynodon 36, 192 ; beak 271 ; 

supratemporal fossa 283 ; teeth 

273 
Didelphia 43 ; general characters 

349 
Didelphyidae 43, 350 ; auditory 

ossicles 486 ; pes 521 ; teeth 423 
Didelphys 43 ; atlas 443 ; teeth 422 
Didus 42 ; see Dodo 
Digitigrade, defined 358 n. 
Digits 26 ; see Manus and Pes 
Dinictrodon 36 ; thoracic vertebrae 

276 

Dinichthys 34, 70 
Dinocerata 364 ; see Uintatheriidae 
Dinornithes 40, 299 ; see Moas 
Dinosauria 38 ; general characters 

204 ; humerus 290 ; ischium 291 ; 

pectoral girdle 288 ; pes 293 ; 

pre-orbital vacuity 284 ; ribs 

285 ; vertebrae 275 f. 
Dinotheriidae 47 



INDEX. 



5.39 



Dinotheriitm 47, 36-5 ; dental for- 
mula 434 ; teeth 345 

Diodon 33 ; beaks 111, D. hystrix, 
scales 105 

Diphycercal tail 60, 116 

Diphyodont, defined 7, 344 

Diplacanthitis 32, 64 

Dipneumona 34 

Dipnoi 34 ; general characters 69 ; 
pelvic fins 131 ; skull 124 ; spinal 
column 113 ; tail 116 ; teeth 111 

Dipodidae 47 

Diprotodont 423 

Diprotodontia 43 ; characters 350 

Dipteridae 34, 70 ; cranium 124 ; 
tail 117 ; teeth 111 

Dipn* 47 ; cervical vertebrae 446 ; 
pes 526 

Discoglossidae 56 

Discoglossm 36 ; ribs 182 ; verte- 
brae 172 

Distal, defined 23 n. 

Divers 40; thoracic vertebrae 332 

Docidophryne 36 ; shoulder girdle 
and sternum 183 

Dodo 42 ; wing 338 

Dog 48; arm bones 4O7 ; an- 
terior limb 405 ; atlas and axis 
379; cranium 384, 389, 396; 
dentition 375 ; innominate bone 
41O; leg bones 411; manus 
408, 413, 511; pectoral girdle 
404: pelvic girdle 409; pes, 413, 
414 ; posterior limb 412 ; ribs 402 : 
second lumbar vertebra 382: 
second thoracic vertebra 382: 
skull 38^, 387; sternum 4O3. 
404; vertebral column 378 

Dogfish 64 ; cranium 73 ) exoskele- 
ton 71 ; median fins 79 ; pectoral 
girdle and fin 79; pelvic girdle 
81 ; pelvic fiu 81 ; ribs 73 ; skull 
73, 75; vertebral column 72; 
visceral skeleton 77 ; Spotted and 
Spiny 32 

Dolphin 4-5, 357; lumbar vertebrae 
448; Gangetic 46, see Pla- 
taniKta 

Donkey, skull 431 

Dorcatheriuin 4-5 ; manus 507 

Dorsal vertebra 16 

Dorsal shield, crocodile 238 

Down feathers 306 



Draco 38; ribs 286 
Dromaeognathous 335 
Dromaeus 40, 299; see Emeu 
Duck 41, 334; beak 329; claws 
330; cranium 313; exoskeleton 
302; pectoral girdle 321; pelvic 
girdle 324, 311, 325; pes, 327; 
posterior Limb 326; ribs 320; 
skull 312, 312, 313; sternum 

321, vertebral column 307; wing 

322, 304. 305 

Duckbill 43; see Ornithorhynchus 
Dugong 44 ; humerus 501 ; pelvi 

514 ; thoraco-lumbar vertebrae 

448 ; see Halicore 
Duplicidentata 48, 366; dental 

formula 435 ; skull 478 

Eagles 335 

Eared Seals 369; scapula 498; see 
Otariidae 

Echidna 43; caudal vertebrae 453; 
manus 504; pelvis 513; sacral 
vertebrae 451; shoulder-girdle and 
sternum 494 ; skull 455 ; spines 
417 ; spur 418 ; thoraco-lumbar 
vertebrae 447 

Echidnidae 43 ; pes 521 

Ectethmoid 21 n. 

Ectocondylar ridge, dog 406 

Edentata 43 ; auditory ossicles 487 ; 
arm bones 500 ; caudal vertebrae 
453 ; cervical vertebrae 443 ; ma- 
nus 504 ; pectoral girdle 495 ; pes 
522 ; pelvis 513 ; ribs 491 ; sa- 
crum 452; skull 457; sternum 
489; teeth 424; thigh and shin 
517; thoraco-lumbar vertebrae 
447 

Eel 33 ; scales 105 

Elasmobranchii 31 ; cranium 118 f. ; 
clasper 132; general characters 
61 ; pelvic fins 131 ; ribs 125 ; 
teeth 109; vertebral column 113 f. ; 
visceral arches 120 

Elasmotlwrium 46 ; mesethrnoid 470 

Elephant 47 ; auditory ossicles 487; 
caudal vertebrae 453 ; ribs 491 ; 
skull 473 f., 474 and 475; tusks 
420 ; see also Proboscidea 

Elephantidae 47 



E. planifront 435; see Elephant 



540 



INDEX. 



Elflinia 36; skull 191, 283 

Embolomerous 172 

Emeu 40, 299 \ aftershaft 328; 

claws 330 

Enamel 4 ; cap 7 ; organ 7 
Endochondral ossification 11 
Endoskeleton, Amphibia 170; birds 

331 f . ; cod 83 f. ; crocodile 239 f. ; 

dog 377 f. ; dogfish 71 f. ; duck 

306 f.; fish 112 f. ; frog 151 f.; 

mammals 442 f. ; newt 138 f. ; 

reptiles 275 f. ; turtle 218 f . 
Engystomatidae 36 
Entoplastron, turtle 217 
Epauorthidae 43, 350 
Epi-branchial, cod 101 ; dogfish 78 ; 

salmon 94 
Epicoracoid 25 ; frog 163 ; turtle 

232 ; Monotremes 493 ; vestiges 

of in Eodentia 497 
Epicrium 35 ; orbit 179 
Epidermal exoskeleton, birds 328; 

crocodile 237; dog 374; duck 

302 ; mammals 416 ; reptiles 

270; turtle 214 
Epi-hyal, cod 100 ; dog 399; salmon 

94 
Epi-otic 20 ; cod 96 ; crocodile 250 ; 

Labyrinthodontia 177 ; reptiles 

278 ; salmon 89 ; turtle 227 
Epiphysis 11 
Epiplastron, turtle 217 
Epiprecoracoid, Amphibia 184 ; 

turtle 232 

Epipterygoid, Lacertilia 200; rep- 
tiles 278 
Epipubis, crocodile 267 ; newt 149 ; 

turtle 235 

Episternum 217 ; frog 163 
Equidae 46; mane 416; scapula 

496; skull 471 
Equus 46; see Horse 
Erinaceidae 49 
Erinacnis 49 ; dental formula 440 ; 

pelvic symphysis 515; prester- 

num 490 ; see Hedgehog 
Esocidae 33 

Esox 33; attachment of teeth 107 
Ethmoid 394; see median ethmoid 
Ethmoidal plane 390 ; region 21 
Ethmo-palatine ligament, dog- 
fish 77 
Ethmo-turbinal, dog 395 



Euchirosaurus 35 ; vertebrae 171 
Eustachian canal ; see Canal 
Eusuchia 39; general characters 

212 

Eutheria 43; general characters 351 
Exocaetus 33; pectoral fins 131 
Exoccipital 19 ; cod 97 ; crocodile 
246; dog 386; duck 314; frog 
154; newt 141; salmon 89; 
turtle 224 

Exoskeleton 2 ; Amphibia 168 ; birds 
328; crocodile 237; dog 374; 
dogfish 71; duck 302; fish 104; 
ganoids 66; mammals 442; rep- 
tiles 270; turtle 214 
Extensor side, defined 29 
Extra-branchial, dogfish 79 
Extra-columella, crocodile 251 ; 
turtle 228 

Fabella, dog 412 

Falco 41 

Falcon 41, 335 

Falconiformes 41 

Feathers 3, 328; duck 302 

Felidae 48; claws 418 

Felis 48; dental formula 437; tho- 

raco-lumbar vertebrae 450 
Femoral shield, turtle 215 
Femur 26; crocodile 268; dog 412; 

duck 326; frog 166; mammals 

517 f.; newt 149; ox and rhino- 
ceros 518; turtle 235 
Fenestra ovalis, crocodile 250 f.; 

dog 392; duck 316; frog 157; 

turtle 228 ; rotunda, dog 392; 

duck 316 

Fenestral recess, duck 316 
Fibula 26 ; crocodile 268 ; dog 412 ; 

duck 327; frog 166; newt 149; 

turtle 235 

Fibulare 27 ; see Tarsus 
File-fish 33 ; see Batistes 
Filoplume 306 
Finches 42 
Fins, fish 115; caudal , Cetacea 

453; cod 87; fish 116; Ichthyo- 

sauria 195; median , cod 86; 

dogfish 79; pectoral , cod 103; 

dogfish 79; pelvic , cod 103; 

dogfish 81 
Fin-rays 105, 115; cod 83, 103; 

dogfish 79 



INDEX. 



541 



Firmisternia 36, 185 

Fish, appeudicnlar skeleton 126; 
endoskeleton 112 f. ; exoskeleton 
104; general characters 60 f. ; 
paired fins 127 f. ; ribs 125 f. ; 
skull 117 f. ; spinal column 112 f. ; 
teeth 106 f . 

Fissipedia 48; general characters 
368 

Flamingo 335 

Flexor side, defined 29 

Floating ribs, dog 402; mammals 
490 

Flower, Sir W. H., on succession of 
teeth in elephants 434 

Flying-fish 33; fox 49, 371, skull 
481, see Pteropus ; gurnard 34, 
see Dactylopterus; lemur 48, 
see Galfopithfcus; lizard 38, 
see Draco 

Fontanelle, salmon 89; anterior , 
dogfish 74 ; frog 154 ; posterior , 
frog 154 

Foot, crocodile 269 ; dog 414 ; frog 
167; newt 149 f.; turtle 236 

Foramen : anterior palatine , dog 
401 ; condylar , dog 401 ; cor- 
diforme, reptiles 292 ; ect-epicon- 
dylar , Sphenodon 290; ent-epi- 
condylar 191 n. ; Carnivora 
vera 502; Cebidae 503; Choloe- 
pus 500; Condylarthra 362, 502; 
Creodonta 368; Insectivora 503; 
Lemurs 503; Marsupials 500; 
reptiles 290 ; external mandibular 
, crocodile 258 ; inferior dental 
, dog 399 ; infra-orbital , dog 
401; Rodents 477 ; ilio-sciatic , 
duck 325; internal mandibular 
, crocodile 258 ; internal orbital 
, dog 401; interparietal , 
Labyrinthodontia 173, 177; rep- 
tiles 277; lacerum anterins, 
dog 388, 400; lacerum me- 
dium, dog 402: lacerum pos- 
terius, dog 392, 401; lachrymal 
, dog 394, 401; magnum, 
cod 97; crocodile 257; dog 386, 
402; dogfish 76; duck 314; frog 
154 ; newt 141 ; salmon 89 ; 
turtle 224; mental , dog 399; 
obturator , duck 326; dog 410; 
ophthalmic , dogfish 74; optic 



, dog 400; dogfish 74; orbi- 
tonasal , dogfish 74; ovaJe, 
crocodile 249; dog 400; pneu- 
matic -, duck 323; pneumo- 
gastric , dogfish 76; posterior 
palatine -, dog 401; post -glenoid 
, dog 402; pre-acetabnlar , 
Chiroptera 515 ; rotundum, 
dog 400; stylomastoid , dog 
392 f., 400; thyroid , dog 410; 
trigeminal , duck 316 ; tri- 
osseum, duck 322 

Fore-arm 26; crocodile 265; dog 
406; duck 323; frog 164; newt 
147; turtle 233 

Fossa: cerebellar , dog 392 ; cere- 
bral , dog 392 ; digital , dog 
412 ; floccular , dog 392 ; infra- 
temporal , see lateral temporal 
, lachrymal , Ruminants 
469; lateral temporal , croco- 
dile 257 ; Sphenodon 283 ; ole- 
cranon , dog 406; prescapular 
, dog 405 ; postscapular , dog 
405; post-temporal , Spheno- 
don 283; pterygoid , crocodile 
257; suborbital , Ruminants 
469 ; supra-acetabular , Rumi- 
nants 514; supra-temporal , 
crocodile 249, 256 ; reptiles 283 ; 
supra-trochlear , dog 406 ; tem- 
poral , dog 398; trochanteric 
, dog 412 

Fowl 41, 335; claws 330; skeleton 
3O1 

Fox 48 

Frigate bird 41 ; clavicles 338 

Frog, anterior limb 164; cranium 
155, 157 ; hyoid apparatus 161 ; 
pelvic girdle 165 ; posterior limb 
166; shoulder - girdle and ster- 
num 183; skull 154 f., 155. 
159: teeth 151; vertebral co- 
lumn 152; Common , Edible 
, Fire-bellied , Green -tree 
, Horned , Midwife , 
Painted and Toad 36 

Frontal 19; cod 96; crocodile 249; 
dog 388; duck 314; newt 141; 
salmon 91; turtle 225; seg- 
ment, crocodile 249; dog 388; 
turtle 225 

Pronto-parietal, frog 156 



542 



INDEX. 



Frugivorous bats, manus 512 ; see 

Pteropidae 

Fulcra 67; Polypterus 106 
Furcula296; duck 322 

Gadidae 33 

Gadus 33; see Cod 

Galeopithecidae 48 

Galeopithecus 48, 370; dental for- 
mula 440; iutercentra 450; pel- 
vic sympbysis 515 ; skull 480 

Galesaurus 36, 192 ; teeth 273 

Galeus, 32; occipital joint 118 

Galli 41 

Galliformes 41 

Gallus 41 ; G. bankiva skeleton 3O1 

Gannet, 41 ; wing 339 

Ganoid scales 8, 60, 104 

Ganoidei 32 ; general characters 
and distribution 66 ; pectoral 
girdle 126 ; pelvic fins 132 ; teeth 
110; skull 121 f. ; spinal column 
112 and 114 

Garialidae 39 

Garialis 39, 212 

Garial 210 

Gar pike 33 ; see Lepidosteus 

Gavialis 39 

Gazella 46 

Gazelle 46; skull 468 

Geckoniclae 37 ; see Gecko 

Gecko 37 ; epipubis 293 ; parietals 
277; supra-temporal fossa 283; 
vertebrae 275 

Gibbon 49; ribs 493; skull 482 

Gill-rays, dogfish 78; salmon 95 

Girajf'a 46 

Giraffe 46, 359 ; cervical vertebrae 
445 ; manus 507 ; pes 523 ; ulna 
501 

Giraffidae 46 ; skull 469 

Girdle" bone, frog 156 

Glenoid cavity 25 ; crocodile 263 ; 
ilog 405; duck 322; frog 162; 
newt 146; turtle 232; fossa, 
dog 394 

Globe-fish 33 

Globicephalus 45; cervical vertebrae 
354 ; manus 506 ; skull 463 

Gluteal surface of ilium, dog 410 

Glyptodon 44; carapace 419; cervi- 
cal vertebrae 443 ; caudal verte- 
brae 453 ; mauus 505 ; pelvis 513 ; 



pes 522 ; teeth 425 ; thoraco- 

lumbar vertebrae 447 
Glyptodontidae 44, 352 ; skull 459 ; 

see also Glyptodon 
Gnathostomata 31, 59 
Golden mole 49 ; see Chrysochloris 
Goniopholidae 39 
Goniopholis 39 ; vertebrae 275 
Goose 334 ; beak 329 ; Spur-winged 

41 
Gorilla 49; carpus 512; ribs 493 ; 

scapula 49t); skull 483; thoraco- 

lumbar vertebrae 450 
Gruidae 41 ; see Cranes 
Gruiformes 41 
Guinea-pig 48; tail 454 
Gular shield, turtle 215 
Gulls 42, 335 ; aftershaft 328 
Gymnodontidae 33; beaks 111 
Gymnophiona 35 ; branchial arches 

180; general characters 136 ; ribs 

182; scales 168; skull 177; teeth 

169 ; vertebrae 172 
Gymnura 49 ; teeth 440 ; zygomatic 

arch 481 

Gypogeramis 41 ; claws 330 
Gyrinophilus 35; vertebral column 

171 

Haddock 33 

Hadrosauridae 39 

Hadrosaurus 39 ; skull 284 

Hag or hag-fish 31, 54 f. 

Hair 3 ; dog 374 ; mammals 416 

Halicore 44, 352 ; manus 505 ; skull 

460 ; teeth 425 ; see Dugong 
Halicoridae 44 
Halitheriidae 44 
Halitherium 44, 352 ; femur 518 ; 

pelvis 514 ; teeth 425 
Hallux 26; dog 415; duck 327; 

frog 167 

Hamular process, dog 397 
Hand, crocodile 266; dog 408 f.; 

duck 324 ; frog 165 ; newt 147 ; 

turtle 233 
Hapale 49 

Hapalidae 49, 372 f. ; teeth 441 
Hare 48, 366 ; acetabular bone 

515 ; dental formula 435 ; femur 

520 ; humerus 502 ; pelvis 515 ; 

scapula 497 ; skull 476 ; tail 

454 ; thoraco-lumbar vertebrae 



INDEX. 



543 



449; Cape jumping 47; see 
Pedeteg 

Harpaiiu* 41 ; serrated beak 334 

Harriott* 32, 66 

Hatteria 37, 197; see Sphenodon 

Havers;an cauals 10; system 
10 

Hawks, beak of 330 

Hedgehog 49, 370; auditory ossicles 
488 ; humerus 503 ; presteruum 
490; skull 480; spines 417; see 
Erinaeau 

Hemichordata 30, 50 

HefUatctau 31 ; branchial arches 
63, 12O; vertebrae 114 

Herbivorous dentition 427, 430 

Heron 41, 335; inter-orbital sep- 
tum 333 ; powder down feathers 
329 

Herring 33 

Hesperornis 40, 299; caudal ver- 
tebrae 333 ; clavicles 338 ; teeth 
330 ; wing 338 

Heterocercal tail 60, 116 

Heterodont 7 

Heterostraci 31 ; general character 
54 

Hexanchus 31 ; branchial arches 
63, 121 

Hinge joint 13 

Hipparion 46 ; manns 508 ; pes 
524 

Hippopotamidae 45 

Hippopotamus 4-5, 359; dental for- 
mula 427 ; hair 416 ; mandible 
467 ; manus 506 ; pes 523 ; sca- 
pula 496 ; skull 467 ; teeth 345 

Hoatzin 41 ; see Opisthocomus 

Holocephali 32. 65, 104 ; clasper 
132 : spinal column 113 ; tail 116 ; 
teeth 109 

Holoptychiidae 33 

Holoptychius 33 ; scales 105 

Holostei 33; general characters 68 ; 
teeth 110 ; see Bony Ganoids 

Hominidae 49, 373 

Homo 49 ; see Man 

Homocercal tail 60, 69, 117; codfish 
87 

Homodont, defined 7 

Hoofs 3; 418 

Hoopoe 42, 335 

Hoplopterus, spur 330 



Hornbill 42, 331 ; bony crest 334 ; 
interorbital septum 333 

Horns 3, 417 

Horny plates on palate 418; 
teeth, Lampreys 4; Myxinoids 
57; Ornithorhynchus 4 

Horse 46, 360 ; fibula 519 ; malleus 
487 ; manus 507 ; pes 534 ; skull 
471 ; teeth 345, 430 ; ulna 501 

Howling monkey 49; see Mycetes 

Humerals, duck 303 f. 

Humeral shield, turtle 215 

Humerus 26 ; crocodile 263 ; dog 
405; duck 323; frog 164; newt 
147 ; turtle 232 ; wombat 5OO 

Humming-birds 42, 335 

Humpbacked whale 44, 357 

Hyaena 48, 369 ; hallux 526 ; pol- 
lex 511 ; sacral vertebrae 452 ; 
teeth 437 

Hyaenidae 48 ; humerus 502 

Hyaenodon 48, 368 

Hyaenodontidae 48 

Hyaline cartilage 10 

Hydrochaerus 48 ; teeth 437 ; see 
Capybara 

Hydromys 47; dental formula 436 

Hydrophidae 38 ; scales 270 

Hydropotes 46 ; canines 429 

Hyla 36 ; fronto-parietal fontanelle 
179 ; sternum 184 

Hylidae 36 

Hylobates 49 ; ribs 493 ; skull 482 

Hyoid 21 ; alligator 285 ; Amphibia 
180 ; birds 336 : cod 100 ; croco- 
dile 259; dogfish 77; dog 399; 
duck 320; frog 161; newt 144; 
reptiles 284 ; salmon 94 : turtle 
231, 285 

Hyomaudibular 23 ; cod 100 ; dog- 
fish 78 ; salmon 94 

Hyomoschus i-5 

Hyoplastron, turtle 217 

Hyostylic 61, 119 

Hyotherium 45; teeth 427 

Hyperodapedon37,198; premaxillae 
284 

Hyperoodon 44 ; skull 464 ; sternum 
489 ; thoracic vertebrae 448 

Hypo-branchial, cod 101; dogfish 
78 

Hypo-hyal, cod 100 ; salmon 95 

Hypo-ischium, Lacertilia 292 



544 



INDEX. 



Hypoplastrou, turtle 217 

Hyporachis 328 

Hypsilophodon 39 ; predentary bone 
284 

Hypsodont, defined 345, 429 

Hypural bone, cod 85 

Hyracidae 47 

Hyracoidea 47 ; femur 519 ; general 
characters 362 ; manus 510; nails 
418; skull 472; teeth 432 

Hyracotherium 46 ; manus 508 ; 
scapula 496 

Hyrax 47, 363; see Procavia 

Hystricidae 47 

Hystricomorpha 47; auditory os- 
sicles 488 

Hystrix, 47; auditory ossicles 488; 
see Porcupine 

Ichthyodorulites 106 

Ichthyoidea 35 ; general characters 

134 
Ichthyopsida3J ; general characters 

59 

Ichthyopterygium 130 
Ichthyornis 40 ; mandible 335 ; 

pelvis 341 ; teeth 330 ; vertebrae 

332 

Icnthyormthiformes 40, 300 
Ichthyosauria 37; general charac- 
ters 195 ; ribs 285 
Ichthyosauridae 37 
Ichthyosaurus 37,197; limbs 290; 

palatines 281 ; pectoral girdle 

288 ; position of limbs 28 ; skull 

196 ; teeth 273 ; vertebral column 

275 
Ichthyotomi 31 ; general characters 

62; fins 130 f . ; tail 116 
Iguana 38 ; teeth 273 
Iguanidae 38; zygosphenes 200, 

276 
Iguanodou 39, 208 f . ; jaws 292; 

predeutary 284 ; sternum 288 ; 

teeth 272 f. ; vertebrae 275 
Iguanodontidae 39 
Iliac surface of ilium, dog 410 
Ilium 25; crocodile 266; dog 409 ; 

duck 325 ; frog 165 ; mammals 

513 f. ; newt 149 ; reptiles 291 ; 

turtle 235 
Incisors, dog 376 f. ; mammals 

344 



Incus, dog 393 ; man, dog and 
rabbit 485 

Infra-marginal shield, turtle 215 

Infra-pharyngeal bone, cod 101 

Inia 45 ; cervical vertebrae 444 ; 
lumbar vertebrae 448 

Innominate bone, dog 409 ; mam- 
mals 513 

Insectivora 48 ; arm bones 503 ; 
auditory ossicles 488 ; cervical 
vertebrae 446 ; general characters 
369 f. ; manus 512 ; pelvis 515; 
pes 527 ; sacrum 452 ; shoulder- 
girdle 499; skull 480; sternum 
490; tail 454; teeth 440; thigh 
and shin 520 ; thoraco-lumbar 
vertebrae 450 

Insectivora vera 49; general cha- 
racters 370 

Intercentra 15 ; Galeopithecus 370 ; 
Ichthyosauria 195 ; Labyrintho- 
dontia 172 ; Sphenodon 198 ; 
Talpa 450 

Interclavicle 25 ; crocodile 263 ; 
Monotremata 494 ; reptiles 289 

Intercondylar notch, dog 412 

Intergular shield, turtle 215 

Interhyal, cod 100 

Intermedium 27; see Carpus and 
Tarsus 

Intermuscular bones, cod 86 

Internasal septum, dogfish 76 

Interorbital septum, birds 333 ; 
crocodile 247 ; duck 317 ; reptiles 
277 

Interspinous bones, cod 86 

Intertarsal ankle joint 190 

Intervertebral discs 15, 378 

Ischial tuberosity, dog 411 

Ischium 25 ; crocodile 266 ; dog 
410 ; duck 325 ; frog 165 ; newt 
149 ; turtle 235 

Ischyodus 32, 66 

Ivory 5 

Jacaua 42; see Parr a 
Jacare 39; scutes 271 
Jaws 21 ; cod 98 f. ; crocodile 252 f.; 

dog 395 f. ; dogfish 77 ; duck 317 f.; 

frog 158 f. ; newt 143 f. ; salmon 

93 f. ; turtle 229 f. 
Jerboa 47; cervical vertebrae 446; 

pes 526 



INDEX. 



545 



Joints, kinds of 13 

Jugal 22 ; crocodile 255 ; dog 398 ; 

duck 318 ; turtle 229 
Jugulares 132 

Kangaroo 43 ; dental formula 423 ; 

lumbar vertebrae 447 ; pectineal 

process 513; pes 522; tail 453; 

teeth 345 
Kestrel, claws 330 
Killer 45 ; see Orca 
Kiwi 40; see Apteryx 
Knee-cap, see patella 
Koala 43 ; lumbar vertebrae 447 ; 

pes 522; tail 453 
Kiikenthal, W., on teeth of Cetacea 

426 ; on teeth of Marsupials 422 

Labial cartilage, dogfish 77; Squa- 
tina 119 

Labridae 33 

Lalms33; see Wrasse 

Labyrinthodontia 35 ; buckler 168 ; 
general characters 135 ; inter- 
parietal foramen 173 ; pelvis 187 ; 
ribs 182 ; skull 176 ; teeth 169 

Lacertilia 37 ; general characters 
199 ; pectoral girdle 288 ; skull 
277 ; vertebrae 275 

Lachrymal 20 ; cod 97 ; crocodile 
251 ; dog 394 ; duck 317 ; salmon 
93 

Lacunae 10 

Lagenorhynchus 45 ; skull 462 

Lagostomus 47 ; maxilla 477 

Lambdoidal crest, duck 315 

Lamella of malleus, dog 393 

Lamnidae 32 

Lamprey 31, 55 f. 

Lancelet 30 ; see Amphioxug 

Laridae 42 ; see Gulls 

Larks 42 

Larvacea 30 ; notochord 51 

Latax 48 ; pes 526 

Lateral ethmoid 21 ; cod 97; salmon 
89 f. 

Leathery turtle 37 ; see Dernio- 
chelys 

Lemuroidea 49 ; caudal vertebrae 
454 general characters. 372 ; 
nails 418 ; ribs 493 ; sacrum 452 ; 
skull 482 ; thoraco-lumbar verte- 
brae 450 ; see Lemurs 

R. 



Lemurs, carpus 512 ; pes 527 ; 
teeth 441 ; see Lemnroidea 

Lenticular 485 ; dog 393 

Lepidosiren 34, 70; branchial 
arches 125 ; fins 130 

Lepidosteidae 33 

Lepidosteus 33 ; attachment of 
teeth 108 ; distribution 66 ; pec- 
toral fins 131 ; scales 67, 104 ; 
skull 123 ; tail 117 ; vertebrae 68 

Lepidotus 33 ; teeth 110 

Leporidae 48 

Lepospondyli 35 

Lepus 48 ; see Hare 

Leptoptilus 41 ; see Adjutant 

Lialis37; 289 

Limbs, general account 26 ; modifi- 
cations in position of 28 ; rep- 
tiles 289 

Llama 45, 359 ; cervical vertebrae 
445 ; skeleton 496 ; teeth 428 

Limicolae 42 

Lingual apparatus, lampreys 58 ; 
myxinoids 57 

Lion" 48 

Loemanctus longipes, shoulder girdle 
and sternum 287 

Loggerhead turtle, carapace 216 

Lophiodon 46 ; teeth 345, 429 

Lophiodontidae 46 

Lophiomyidae 47 

Lophiomys 47 ; pes 526 ; skull 476 

Lophius, attachment of teeth 107 

Lower jaw ; see Mandible 

Lumbar vertebrae 16 ; crocodile 
242 ; dog 378 f. ; duck 311 

Lunar 27 ; dog 408 

Macacus 49 ; cervical vertebrae 446 
Machaerodus 48; upper canines 437 
Macrauchenia 46, 358 ; calcaneum 

360 ; cervical vertebrae 445 ; 

fibula 519 ; tarsus 523 ; ulna 501 
Macraucheniidae 46, 509 
Macropodidae 43, 350 ; dental 

formula 423 ; pes 522 
Hacropus 43 ; see Kangaroo 
Macroscelidae 49 
Macroscelides 49 ; skull 480 
Magnum 27 ; see Carpus 
Malar 22 ; see jugal 
Malleus, dog 393 ; man, dog and 

rabbit 485 

35 



546 



INDEX. 



Mammalia 42 ; auditory ossicles 
485 ; cervical vertebrae 442 ; exo- 
skeleton 416 ; general characters 
343; manus 503; Mesozoic 348 ; 
pectoral girdle 493 ; pelvic girdle 
512 ; pes 521 ; ribs 490 ; sacral 
and caudal vertebrae 451 ; skull 
455 ; sternum 489 ; thigh and 
shin 517 ; thoraco-lumbar verte- 
brae 447 

Man 49 ; arm bones 503 ; auditory 
ossicles 488 ; caudal vertebrae 
454 ; cervical vertebrae 446 ; pel- 
vis 515 ; pes 527 ; ribs 493 ; 
scapula 499 ; skull 483 ; sternum 
490 ; teeth 441 

Manatee 44 ; see Manatus 

Manatidae 44 

Manatus 44 ; cervical vertebrae 444 ; 
dental formula 425 ; humerus 
501 ; manus 505 ; pelvis 514 ; 
skull 460 ; sternum 489 ; teeth 
345 ; thoraco-lumbar vertebrae 
448 

Mandible, birds 335 ; cod 100 ; 
crocodile 258 ; dog 398 ; duck 
319 ; frog 160 ; Hippopotamus 
467 ; Isabelline bear 438 ; newt 
144 ; salmon 94 ; turtle 230 

Manidae 44 ; see Mania 

Manis 44 ; auditory ossicles 487 ; 
manus 504 ; scales 3, 417 ; skull 
459 ; M. macrura xiphisternum 
489 ; see Pangolin 

Manubrium of malleus 486 ; dog 
393 ; sterni, dog 404 

Manus 26; crocodile 265 ; dog 408, 
413 ; duck 323 ; frog 164 ; mam- 
malia 503 ; newt 147 ; Perisso- 
dactyles 508 ; turtle 233 

Marginal plate, turtle 216 ; ray 
131 ; shield, turtle 214 

Marmoset 49, 372 f. 

Marmot, frontals 476 

Marsipobranchii 31, 53 ; spinal 
column 56 

Marsupial bones 513 

Marsupial mole 43 ; see Notoryctes 

Marsupialia 43 ; arm bones 499 ; 
auditory ossicles 486; cervical 
vertebrae 443 ; caudal vertebrae 
453 ; general characters 349 ; 
manus 504 ; pectoral girdle 494 ; 



pelvis 513 ; pes 521 ; ribs 491 ; 
sacral vertebrae 451 ; skull 456 ; 
teeth 422 ; thigh and shin 517 ; 
thoraco-lumbar vertebrae 447 

Mastodon 47, 365 ; teeth 434 

Mastodonsaurus 35, 136 ; pelvis 187 

Mastoid portion of periotic, dog 
391 

Maxilla 22 ; cod 98 ; crocodile 254 ; 
dog 397 ; duck 318 ; frog 159 ; 
newt 144 ; turtle 229 

Maxillo-mandibular arch 21 

Maxillo-palatine, duck 318 

Maxillo-turbinal, dog 395 

Meatus, external auditory , cro- 
codile 250 ; dog 393 ; turtle 228 ; 
internal auditory , crocodile 
251 ; dog 392, 400 ; turtle 228 

Meckel's cartilage 22 ; cod 100 ; 
dogfish 77 ; salmon 94 

Median ethmoid 21 ; cod 98 ; Gym- 
nophiona 179 ; salmon 91 ; 
fin, Amphibia 52 ; cod 86 ; dog- 
fish 79 

Megachiroptera 49; general charac- 
ters 371 

Megalobatrachiiis 35, 135 ; carpus 
186 ; skull 175 

Megalosauridae 38 

Megalosaurus 38, 208 

Megapodius, spur 330 

Megaptera 44, 357 

Megatheriidae 44, 352 ; humerus 
501 ; leg bones 517 ; pelvis 513 ; 
sacrum 452 ; teeth 424 ; thoraco- 
lumbar vertebrae 447 

Megatherium 44 ; femur 517 ; ma- 
nus 505 ; pectoral girdle 495 ; 
pes 522 ; skull 458 

Megistanes 40, 299 

Membranous cranium 17 

Menobranchidae 35 

Menobranchus 35, 135 ; carpus 185 : 
pes 188 ; skull 174; teeth 1(59 

Menoporna 35 ; see Cryptobrtnidnt* 

Mento-meckelian 22 ; frog 161 : 
reptiles 284 

Merganser 41 ; beak 329 

Merijit* 41 

Merrythought, duck 322 

Mesethmoid 20 ; dog 390 ; duck 
317 

Mesophdon 44 ; teeth 427 



INDEX. 



547 



Meso-pterygium 79 

Mesosauridae 37 

Meso.iaiints 37 

Mesosternum, dog 404 

Metacarpal quill, duck 303 

Metacarpo-digital, duck 303 

Metacarpus 2ti ; see Manus 

Metacromion, hares and rabbits 
497 

Meta-pterygium 79 

Metatarsus 26 ; see Pes 

Metatheria 43 ; general characters 
349 

Metriorhynchus 39, 278 

Microchiroptera 49 ; general cha- 
racters 371 

Microgale 49 ; caudal vertebrae 454 

Mid-digital quill, duck 303 

Milk-teeth 344 ; dog 377 ; horse 
430 

Moa 40, 299 ; aftershaft 328 ; pec- 
toral girdle 336 ; wing 338 

Molar teeth 344 ; dog 376 f. 

Mole 49, 370 ; auditory ossicles 
488 ; cervical vertebrae 446 ; 
humerus 503 ; manus 512 ; pre- 
sternum 490 ; shoulder girdle 
499 ; skull 481 ; teeth 440; Golden 
49 ; see Chrtjfochloris ; Mar- 
supial 43 ; see Xotoryctes 

Molge 35, 135 ; see Newt 

Monitor 36' ; see Varanus 

Monkey 49, 373 ; see under Pri- 
mates 

Monodelphia 43 ; characters of 351 

Monodon 4-5, 367 ; see Narwhal 

Monophyodont, denned 7 ; 344 

Monopneumona 34 

Monotremata 42 ; arm bones 499 ; 
auditory ossicles 486 ; caudal 
vertebrae 453 ; cervical vertebrae 
443 ; general characters 346 ; 
manns 504 ; pectoral girdle 493 ; 
pelvis 513 ; pes 521 ; ribs 490 ; 
sacral vertebrae 451 ; skull 455 ; 
sternum 489 ; teeth 422 ; thigh 
and shin 517 ; thoraco-lumbar 
vertebrae 447 

Morosaurus 38, 207 ; pes 294 

Mosasaurus 38, 204 

Moschug 46 ; canines 429 

Mouse 47 ; teeth 437 ; see J/M* 

Mud-fish 3^ 



Multituberculata 43, 348 

Muntjac 46; "see Cervulus 

Muraenidae 33 

Muridae 47 

Mu." 47 ; J/. musculus, teeth 437 ; J/. 

sylvaticus, sternum and shoulder 

girdle 498 

Musk deer 46 ; canines 429 * 
Mustelidae 48 ; teeth 439 
Mycetes 49 ; hyoid 485 ; mandible 

484 ; skull 482 
Myliobatidae 32 ; teeth 109 
Myomorpha 47 
Myrmecobiu*, teeth 423 
Myrmecophaga 44 ; manus 505 ; 

pectoral girdle 495 ; skull 458 
Myrmecophagidae 44, 424 ; see 

Anteaters 
Mystacoceti 44 ; general characters 

356 ; hind limb 518 ; manns 

505 ; pectoral girdle 495 ; skull 

461 ; teeth 426 
Hyjcine 31, 55 ; fins 115 ; noto- 

chordal sheath 9 
Myxinoidei 31, 55 

Nails 3 ; Amphibia 168 ; mammals 
417 

Nares : anterior , crocodile 252, 
257 ; dog 401 ; duck 317 ; newt 143 ; 
turtle 225, 229 ; posterior , cro- 
codile 257 ; dog 402 ; duck 318 ; 
frog 158 ; newt 143 ; turtle 230 

Narial cavity, salmon 89 ; pas- 
sage, crocodile 254 ; dog 395; 
septum, dog 401 

Narwhal 4-5, 3-57 ; teeth 427 

Nasal 21 ; crocodile 252 ; dog 394 ; 
duck 317 ; frog 158 ; newt 143 : 
turtle 228; capsule 20; cod 97 ; 
crocodile 252 ; dog 394 ; dogfish 
74 ; frog 158 ; newt 143 ; turtle 
228 ; cavity, dog 388 ; fossae, 
salmon 89 ; horns, rhinoceros 3 

Navicular 27 ; dog 414 

Neornithes 40 ; general characters 
B8 

Netodon 46, 361 ; pes 525 ; teeth 
432 

Nesodontidae 46 

Neural arch 14; plate, turtle 
215 ; spine 14 

Neuromere, denned 112 

352 



INDEX. 



Newt 35 ; anterior limb 147 ; byoid 
apparatus or visceral arches 144, 
181 ; pelvic girdle 149 ; ribs 
145 ; shoulder girdle 146 ; skull 
140 ; sternum 145 ; vertebral 
column 138 

Notidanidae 31 ; calcification of 
vertebrae 114 ; pectoral fins 130; 
vertebral column 113 ; visceral 
arches 63, 119 f. 

Notochord, Amphioxus 52 ; Balano- 
glossus50; dogfish 72; Tunicates 
51 

Nothosaurus 37, 193; supratemporal 
fossae 283 

Nothosauridae 37 

Notoryctes 43; arm bones 500; 
caudal vertebrae 453 ; cervical 
vertebrae 443 ; claws 418 ; dental 
formula 423 ; manus 504 ; pelvis 
513 ; pectoral girdle 494 ; pes 
521 ; ribs 491 ; sacrum 452 ; 
skull 457 ; sternum 489 ; thigh 
and shin 517 

Notoryctidae 43, 350 

Nuchal plate, turtle 215 ; shield, 
crocodile 238 ; turtle 214 

Nyrania 35 ; palatines 177 

Occipital condyle, crocodile 246 ; 
dog 386; duck 315; frog 154; 
turtle 224; crest, dog 386; 

segment, crocodile 246 ; dog 
384 ; turtle 224 

Odontaspis 32 ; succession of teeth 

1O7 

Odontoblast 7 
Odontoceti 44; general characters 

357 ; manus 505 ; pectoral girdle 

495; skull 462; sternum 489; 

teeth 426 
Odontolcae 40 ; general characters 

299 

Odontopteryx 40; jaws 334 
Oginorhinus 48 ; mandibular ramus 

439 
Olecranon process, dog 406 ; duck 

323 ; frog 164 
Olfactory capsule, see nasal capsule ; 

cavity, dog 388 ; chamber, 
dog 395 ; fossa, dog 390 

Olm35 

Omosaurus, exoskeleton 272 



Omosternum, frog 163 

OnycJiodactylits 35 ; nails 168 

Operculum, cod 101; salmon 95 

Ophidia 38 ; general characters 202 ; 
jaw bones 280 ; scales 270; skull 
277 f. ; vertebral column 275 

Ophisaurus 38; limbs 289; pectoral 
girdle 289 

Opisthocoelous, defined 14 

Opitthocomus 41 ; skull 334 

Opisthotic 20 ; cod 96 ; crocodile 
250 ; salmon 89 f. ; turtle 227 

Opossum 43; caudal vertebrae 453; 
teeth 423 

Optic capsule 20 ; crocodile 251 ; 
dog 394 ; turtle 228 

Orang 49 ; carpus 512 ; ribs 493 ; 
thoraco-lnmbar vertebrae 450 

Orbit, crocodile 257 ; dogfish 74 ; 
duck 317 

Orbital ring, cod 97 ; salmon 93 

Orbitosphenoid 19 ; dog 388 ; duck 
317 ; newt 141 

Orca45; teeth 427 

Oreodon 45 ; see Cotylops 

Ornithodelphia 42 ; general charac- 
ters 346 

Ornithosauria 212 

Ornithorhynchidae 43 

Ornithorhynchus 43; beak 3, 418; 
caudal vertebrae 453 ; manus 
504 ; pelvis 513 ; sacral vertebrae 
451 ; shoulder girdle 347 ; skull 
455 ; spur 418 ; tarsus 27 n. ; teeth 
4, 346, 422 ; thoraco-lumbar ver- 
tebrae 447 

Ornithopoda 39 ; general characters 
209 

Orthopoda 39 ; general characters 
208 ; pubes 292 

Orycteropodidae 44 ; teeth 425 

Orycteropits 44 ; hair 416 ; manus 
505 ; pectoral girdle 495 ; pelvis 
513 ; skull 459 ; see Aard Vark 

Osborn, H. F., on Mesozoic Mam- 
mals 348 

Os entoglossum, duck 320 

Osteoblast 11 

Osteoclast 11 

Osteodentine 108 

Osteostraci 31 ; general characters 
54 

Ostracion 33, 69 ; plates 105 



INDEX. 



549 



Ostracionidae 33 

Ostracodermi 31 ; general charac- 
ters 54 

Ostrich 40, 299; aftershaft 329; 
cervical vertebrae 331 ; claws 
330; foot 342; manus 338; pelvic 
girdle and sacrum 34O ; pubis 
341 ; tibio-tarsus 341 ; wing 
339 

Otaria 48; dentition 439; tym- 
panic bulla 480 

Otariidae 48, 369 ; auditory ossicles 
488 ; scapula 498 ; skull 480 

Owen's apteryx, pelvic girdle and 
sacrum 34O 

Owen's chameleon, epidermal horns 
271 

Owls 42, 335 ; aftershaft 329 ; foot 
342 

Owl-parrot 42 ; see Stringops 

Ox 46, 359; atlas and axis 445; 
three cervical vertebrae 15 ; fe- 
mur 518; manus 507; teeth 
345 ; two thoracic vertebrae 449 

Paca J> 

Paired fins 127 
Palaeoniscidae 32 
Palaeonisciu 32 ; scales 67 
Palaeospondylidae 31 
Palaeoxpondyhis 31, 58 
Palaeosyop* 46 ; teeth 432 
Palaeotheriidae 46 
Palaeotheriiim 46 ; skull 471 ; teeth 

430 

Palamedea 41 ; spur 330, 338 
Palamedeae 41 
Palate, reptiles 280 f. 
Palatine, cod 98 ; crocodile 254 ; 

dog 397; duck 318; frog 160; 

salmon 93 ; turtle 230 
Palato-pterygo- quadrate bar 22; 

dogfish 77; fish 120 f. ; salmon 

93 

Palm civet 48 
Pangolin 44 ; pectoral girdle 495 ; 

pelvis 513 ; caudal vertebrae 453 ; 

see Manis 
Parachordals 17 
Paradoxurus 48; tail 454 
Parasphenoid 21 ; cod 97 ; frog 

156 ; newt 141 ; reptiles 278 ; 

salmon 93 



Parasuchia 3d ; general characters 
211 

Parethmoid 21 n. 

Pariasauria 36 

Pariasaurus 36, 192; pectoral girdle 
289 ; pelvis 292 ; supratemporal 
fossa 283 ; teeth 273 

Parietal 19 ; cod 96 ; crocodile 
247; dog 386; duck 314; newt 
141 ; salmon 91 ; turtle 225 ; 
segment, crocodile 247 ; dog 386 ; 
turtle 225 

Paroccipital process, dog 386 

Parra 42 ; spur 330 

Parrots 335; aftershaft 328; beak 
330 ; epiphyses of centra 332 ; 
foot 342 ; powder-down feathers 
329 ; skull 334 

Parrot fish 33; see Scar us 

Passeres, aftershaft 328 

Passeriformes 42 

Patella, dog 412 ; duck 327 

Paro 41 ; P. cristatus, shoulder 
girdle and sternum 337 

Peacock 41 ; see Paro 

Peccary, pes 523 

Pecora 46, 359 ; teeth 429 

Pectinated incisors, Galeopithecus 
370, 440 ; Procavia 362 

Pectineal process, duck 326 

Pectoral fins, cod 103 ; dogfish 79 ; 
girdle 24 ; Amphibia 184 ; 
birds 336; cod 101; crocodile 
262 ; dog 404 ; dogfish 79 ; duck 
321; fish 126; frog 162; mam- 
malia 493 ; newt 145 ; reptiles 
288 ; turtle 231; shield, turtle 
215 

Pedetes 47; manus 511; tail 454 

Pelican 41, 335 ; clavicles 338 

Pelicaiius 41 ; P. conspic Hiatus 
shoulder girdle and sternum 
337 

Pelobates 36; vertebrae 172; P. 
cultripes teeth 169 

Pelobatidae 36 

Pelvic tins, cod 103; dogfish 82; 
fish 131 ; girdle 25 ; Amphi- 
bia 187 ; birds 339 ; crocodile 266 ; 
dog 409 ; dogfish 81 ; duck 324 ; 
fish 127 ; frog 165 ; mammals 
512; newt 149; Ratitae 34O; 
Reptilia 291 ; turtle 235 



550 



INDEX. 



Penguin 40; distribution of feathers 
328 ; fibula 341 ; foot 342 ; manus 
338 ; metatarsus 342 ; pneuma- 
ticity of skeleton 331; skull 333; 
sternum 336 ; thoracic vertebrae 
332 ; wing 329, 339 

Penna, duck 303 

Pentedactylate, defined 26 

Perameles 43; atlas 443; pectoral 
girdle 494 

Peramelidae 43, 350; auditory os- 
sicles 486 ; pes 522 

Perca 34 

Perch 34 ; pelvic fin 132 ; urostyle 
117 

Percidae 34 

Perennibranchiata 35 ; characters 
135 

Perichondrium 10 

Perichordal sheath 16 

Periosteal ossification 10 

Periosteum 10 

Periotic, dog 390; capsule, see 
Auditory capsule 

Perissodactyla 46; cervical verte- 
brae 445 ; general characters 
359 ; manus 507 ; pes 523 ; ribs 
491; scapula 496; skull 470; 
teeth 429 ; thoraco-lumbar ver- 
tebrae 448 

Persistent pulps 5 

Pes 26; crocodile 268; dog 413, 
414 ; duck 327 ; frog 166 ; mam- 
mals 521; reptiles 293; turtle 
236 ; of Tapir, Ehiuoceros, Hip- 
parion and Horse 524 

Petromyzon 31, 55 f. ; notochordal 
sheath 9 

Petromyzontidae 31, 55 

Petrous portion of periotic, dog 
391 

Pezophaps 42 ; see Solitaire 

Phacochaerus 45 ; teeth 428 

Phaethon 41 ; metatarsals 342 

Phalacrocorax 41 

Phalangeridae 43, 350 

Phalanges 26 ; see Manus and 
Pes 

Phaneroglossa 36 

Pharyngo-branchial, cod 101 ; dog- 
fish 78 ; salmon 95 

Pharyngognathi 33 

Phascolarctus 43 ; see Koala 



Phascolomyidae 43, 350 

Phascolomys 43, 349 ; see Wombat 

Phascolotheriuin 43, 348 

Phenacodontidae 47 

Phenacodus 47, 362 ; caudal ver- 
tebrae 454 ; manus 5 1O ; pes 
525; scapula 497; skull 472; 
thoraco-lumbar vertebrae 449 

Phocaena 45, 357 ; skull 462 ; tho- 
raco-lumbar vertebrae 448 ; P. 
phocaenoides, ossicles 420 

Phocidae 48, 369; scapula 497; 
tympanic bulla 480 

Phoronis 30, 50 f . 

Phororhaeos 41 ; anterior nares 
333; ischia 341 

Physeter 44 ; cervical vertebrae 
444; manus 505; skull 464; teeth 
426 

Physeteridae44; ribs 491; thoraco- 
lumbar vertebrae 448 

Physodon 44 ; teeth 426 

Physodontidae 44 

Physostomi 33 

Phytosauridae 39 

Phytosaurus 39; see Belodon 

Pici 42 

Picus 42; see Woodpecker 

Pig 45, 359; skull 465 f., 466; 
teeth 345, 427 

Pigeons 42, 334 f.; aftershaft 329; 
pneumaticity of skeleton 331 

Pike 33 ; pelvic fin 132 ; teeth 107, 
110 

Pinnipedia 48; arm bones 502; 
auditory ossicles 488; general 
characters 369; manus 511; 
pelvis 515; pes 526; skull 480; 
teeth 439 ; thigh and shin 520 ; 
thoraco-lumbar vertebrae 450 

Pipa 36; hyoid apparatus 182; 
jaws 169; skull 180; sternum 
184 ; vertebrae 172 

Pipidae 36 

Pisces 31 ; general characters 60 

Piscivorous dentition 426, 440 

Pisiform 345, 504; crocodile 265; 
dog 408 ; turtle 233 

Pituitary fossa, crocodile 247 ; 
space 17 

Placodontia 36 

Placodus 36, 192; teeth 273 

Placoid scale 4, 60, 104 



INDEX. 



551 



Plantigrade, defined 358 n. 

Plastron, Dermochelys 272; Che- 
lone midas 217, 318, 271 

Platanistidae 4-5 

Platanista 43, cervical vertebrae 
444; skull 464 

Plectognathi 33 ; vertebrae 115 

Plectropterus 41; P. gambensis, 
spur 330 

Plesiosauridae 37; limbs 193 ; para- 
sphenoid 192; sknU278 

Plesioiaurus 37, 193: position of 
limbs 28 

Pleuracanthidae 63; fins 115 

Pleurodira 37; general characters 
195 

Pleurodont, 159, 199, 273 

Pleuronectidae 33 

Pleuropterygii 31, 63 

Pliosaurus~37, 193 

Plovers, 42, 334 ; thoracic verte- 
brae 332 

Pneomaticity of bird's skeleton 331 

Polacanthus 39; exoskeleton 272 

Pollex 26 ; see Manns 

Polyodon 32, 104 ; distribution 66 ; 
pectoral fins 131; skull 122; 
spinal column 112 ; teeth 110 

Polyodontidae 32 

Polyonax 39, 209; beak 271; 
frontals 277; jaw 274 ; predentary 
2*4 

Polyprotodont 423 

Polyprotodontia 43; general cha- 
racters 350 

Polypteridae 33 

Polypteru* 33, 68 ; distribution 66 ; 
esoskeleton 67; pectoral fins 
131 ; pelvic fins 132 ; pelvis 
127 : scales 104 ; skull 122 ; tail 
116 

Pontoporia 46; cervical vertebrae 
444: teeth 426 

Porcupine 47 ; pes 526; skull 476, 
477 ; spines 417 

Porpoise 46, 367; thoraeo-lumbar 
vertebrae 448 

Postaxial 28 

Posterior cornu, duck 320; turtle 
231; limb 26; Amphibia 188; 
birds 341; dog 412; duck 326; 
frog 166; newt 149, 148 ; reptiles 
293; turtle 235, 234 



Postfrontal 21 ; crocodile 250 ; 
turtle 225 ' 

Postorbital bar, crocodile 250, 
255 f.; Hatteria 283; groove, 
dogfish 76 

Post-temporal, cod 102 ; reptiles 
283 ; bar, crocodile 256 ; Hat- 
teria 283 

Potamogale 49, 367, 370; shoulder 
girdle 499; teeth 440 

Potamogalidae 49 

Powder-down feathers 329 

Pre-axial 28 

Precoracoid 25 ; frog 163 : newt 147 ; 
reptiles 288; turtle 232 

Predentary, reptiles 284 

Predigital quill, duck 303 

Prefrontal 21 ; crocodile 249 ; rep- 
tiles 278 ; turtle 225 

Prefronto-lachrvmal, newt 141 

Prehallux, frog"l67 f. 

Premaxilla 22; cod 98; crocodile 
252: dog 398; duck 314, 318; 
frog 158 ; newt 143 ; salmon 94 ; 
turtle 230 

Premolar, dog 370, 377; mammals 
344 

Prenasal process, frog 158 

Pre-orbital vacuity, reptiles 283 

Presphenoid 19 ; dog 388 

Prespiracnlar ligament, dogfish 77 

Presternum, dog 404 

Primaries, duck 303 

Primates 49; arm bones 503; au- 
ditory ossicles 488 ; cervical ver- 
tebrae 446; general characters 
372; manus 512; pelvis 515; 
pes 527; ribs 493; sacrum 452; 
shoulder girdle 499 ; skull 482 f.; 
sternum 490 ; tail 454 ; teeth 
441 ; thigh and shin 520 ; thora- 
co-lumbar vertebrae 450 

Priodon 44; caudal vertebrae 453; 
manus 505 ; stapes 487 ; sternum 
489; teeth 424 

Pristidae 32 

Pristis 32; snout or rostrum 109. 
119 

Proboscidea 47; arm bones 502; 
cervical vertebrae 445 : general 
characters 364 ; femur 519 ; ma- 
nus 511; pelvis 514; pes 526; 
scapula 497; skull 473; teeth 



552 



INDEX. 



433; thoraco- lumbar vertebrae 
449 

Procavia47, 363; auditory ossicles 
487; caudal vertebrae 453; dental 
formula 432 ; humerus 502; ma- 
nus 51O; pelvis 514; pes 525; 
ribs 491 ; scapula 497 ; skull 
433, 472; tarsus 27; thoraco- 
lumbar vertebrae 449 

Process, alinasal , frog 158 ; 
basi-pterygoid , birds 334 ; 
coracoid , dog 405 ; corouoid 
(of mandible), dog 398; duck 
319; coronoid (of ulna), dog 
408 ; pectineal , duck 326 ; post- 
frontal , duck 316; postgle- 
noid , dog 394 ; postqrbital 
(of frontal), dog 388; postorbital 
(of jugal), dog 398; posterior 
articular , duck 319; zygo- 
matic , dog 394 

Processus brevis, 486; gracilis 
486; longus, 486; dog 393 

Procoelous, denned 14 

Prodelphinus 45; skull 462 

Proganosauria 37 

Prone position 29 

Prongbuck 46 ; horns 417 

Pro-otic 20; frog 157; turtle 227 

Pro-pterygium, dogfish 79 

Proteidae 35 

Proteles 48; teeth 437 

Protelidae 48 

Proterosauridae 37 

Proterosaums 37; teeth 198, 274; 
vertebrae 197 

Proteus 35, 135, 182; branchial 
arches 180 ; digits 187 ; pes 188 ; 
skull 174 

Protopterus 34, 70. 117; branchial 
arches 121, 124; fins 130; skull 
124; vestigial gill on pectoral 
girdle 129 

Prototheria 42; general characters 
346 

Proximal, defined 23 n. 

Psephurus, distribution 66 

Pseudopus 38 ; limbs 289 

Psittaci 42; see Parrots 

Pteranodon 39, 274 ; pectoral girdle 
289 

Pteranodontidae 39 

Pteraspia 31, 54 



Pterichthys 31, 55 

Pterocles 42 ; see Sandgrouse 

Pteroclidae 42 

Pterodactylidae 39 

Pterodactylus 39, 213 

Pteropidae 49; skull 481 

Pteropus 49; dental formula 441; 

tail 454 
Pterosauria 39; general characters 

212; ischia292; limbs 291; pre- 

orbital vacuity 284; ribs 285; 

sternum 287 ; vertebrae 275 f. 
Pterotic20; cod 96; salmon 90 f. 
Pterygoid, cod 98; crocodile 255; 

dog 397; duck 318; frog 160; 

newt 144; salmon 93 ; turtle 230 ; 

fossa, crocodile 255 ; plate, 

dog 388 
Pterylae 328 
Pubis 25; crocodile 266 f.; duck 

325; dog 411; frog 165; newt 

149 ; reptiles 292 ; turtle 235 
Pygal plate, turtle 217 ; shield, 

turtle 214 
Pygopodidae 37 
Pygostyle, duck 307, 312 
Python 38; ischio-pubis 292; jaws 

280 ; vestiges of limbs 289, 293 
Pythonomorpha 38; general cha- 
racters 204; limbs 290; teeth 

273 

Quadrate 22; cod 98; crocodile 
255; duck 319; frog 160; newt 
144 ; salmon 93 ; turtle 229 

Quadratojugal 22 ; crocodile 255 ; 
duck 318; frog 160; turtle 229 

Quill, duck 302 

Eabbit 48, 366; pollex 511 
Kaccoou 369 
Bachis, duck 302 
Eachitomous, defined 171 
Eadiale 27 ; see Carpus 
Eadialia 115; dogfish 79 f. 
Eadio-ulna, frog 164 
Eadius 26; crocodile 265; dog 406; 

duck 323 ; newt 147 ; turtle 233 
Eaia 32 ; calcification of vertebrae 

114 

Eaiidae 32 
Rana 36 ; see Frog 
Eanidae 36 ; shoulder girdle 185 



INDEX. 



553 



Rat, pes 526 

Ratitae 40; caudal vertebrae 333; 
clavicles 338; foot 342; general 
characters 298; skull 333; ster- 
num 336 ; vomers 334 ; wing 338 

Rattlesnake 38; rattle 3, 270 

Ray. pectoral fin 130; Eagle , 
Electric and Sting , 32 

Rectrices, 303, 329 

Reed-fish 33 

Reindeer, antlers 469 

Remicle, duck 304 

Remiges, 303, 329 

Reptiles, anterior limb 290; exo- 
skeleton 270; fossae in skull 281 ; 
pectoral girdle 288 ; pelvic girdle 
291; posterior limb 293; ribs 
285; skull 276; sternum 287; 
teeth 272 ; vertebral column 275 

Reptilia 36 ; general characters 190 ; 
see Reptiles 

Rhabdopleura 30, 50 

Rhamphastos 42; see Toucan 

Rhamphorhynchidae 39 

Rhamphorhynchus 39, 213, 274 

Rhea 40; aftershaft 329; claws 
330; ischia341; manus 338; R. 
macrorhyncha, pelvic girdle and 
sacrum 34O 

Rheornithes 40 

Rhina 32; see Squatina 

Rhinal process, frog 158 

Rhinoceros 46, 360, 419; femur 
518; fibula 519; malleus 487; 
manus 508; nasal horns 3, 417; 
pes 525; skull 431, 470; teeth 
430; ulna 501; R. antiquitatis 
470 

Rhinocerotidae 46 

Rhinolopbidae 49 

Rhiptoglossa 38 

Rhizodontidae 33 

Rhizodus 33; teeth 110 

Rhynchocephalia 37; general cha- 
racters 197 ; humerns 290 ; teeth 
273 f. ; vertebrae 275 

Rhynchosauridae 37 ; maxillae 198 

Rhytina 44, 352, 425; humerus 
501; skull 460 

Rhytinidae 44 

Ribs 23; Amphibia 182; birds 336; 
cod 86 ; crocodile 259 ; dog 402 ; 
dogfish 73 ; duck 320 ; fish 125 ; 



frog 153; mammalia 490; newt 
145 ; reptiles 285 

Ridge, supra-orbital andsuborbital, 
dogfish 74 

Rodentia 47; auditory ossicles 488; 
cervical vertebrae 446 ; dental 
formula 435 ; general characters 
365 ; pelvis 515 ; pes 526 ; hume- 
rus 502 ; manus 511 ; ribs 493 ; 
sacrum 452 ; shoulder girdle 497 ; 
skull 476; sternum 489; tail 
454; teeth 421; thigh and shin 
520 ; thoraco-lumbar vertebrae 
449 

Roller 42, 335 

Rooted teeth, defined 5 

Rorqual 44, 357; cervical vertebrae 
444 

Rostrum, crocodile 247; dogfish 
74; duck 316; PristisllQ; of 
sternum, duck 321 

Rose, C., on teeth of Marsupials 
422 

Ruminantia 46, 359; auditory os- 
sicles 487; fibula 519; horny 
plates on palate 418 ; hyoid 470 ; 
manus 507 ; odontoid process 
445 ; pes 523 ; scapula 495 ; teeth 
420, 429 

Sabre-toothed lion 48, see Machae- 
rodus 

Sacral ribs, crocodile 243 ; sur- 
face of ilium, dog 409 ; verte- 
brae 16; crocodile 243; dog 383; 
duck 312; frog 153; newt 140; 
turtle 222 

Sacrum, duck 310 ; see Sacral ver- 
tebrae 

Sagittal crest, dog 386 

Saiga, skull 468 

Salamander 35 

Salamandra 35, 135; antibrachiuin 
and manus of larva 186 ; manus 
of larva 185 ; tarsus 27 

Salamandrina 3-5, 135; skull 175; 
sternum 182 

Salmo 33 

Salmon 33 ; branchial arches 95 ; 
chondrocranium 87 ; opercnlar 
bones 95; pectoral fins 131 ; skull 
87 

Salmonidae 33 



554 



INDEX. 



Sandgrouse 42, 335 
Sarcophilus 43 ; teeth 423 
Sauropoda 38 ; general characters 

205 ; teeth 273 ; vertebrae 276 
Sauropsida 36; general characters 

189 

Sauropterygia 37; general charac- 
ters 192; limbs 290; palate 281; 

pectoral girdle 288; vertebrae 

276 

Saw-fish 32 ; see Pristis 
Scales, cod 83 ; crocodile 237 ; 

ctenoid 8 ; cycloid 8 ; duck 302 ; 

ganoid 8 ; Gymnophiona 168 ; 

mammals 417 
Scale-foot 37 
Scalpriform 366 

Scaphirhynchus 32, 104 ; distribu- 
tion 66; exoskeleton 67; spinal 

column 112 

Scaphoid 27 ; mammals 504 f . 
Scapho-lunar, dog 408 
Scapula 25 ; cod 103 ; crocodile 263 ; 

dog 404; duck 322; frog 162; 

newt 146 ; turtle 232 
Scapular shield, armadillo 419 
Scapus, duck 302 
Scams 33; beaks 111 
Scelidosauridae 39 
Schizoguathous, denned 335 
Scincidae 38 
ttcincus 38 ; scutes 271 
Sciuromorpha 47 
Sclerotic, turtle 228 
Screamer 41 ; spurs 330 
Scutes, armadillos 419 ; crocodile 

237 ; reptiles 271 
Scylliidae 32 

Scyllium 32 ; calcification of ver- 
tebrae 114 ; pectoral fins 130 ; 

suspensorium 119; see Dogfish 
Scymnua 32, 118 ; calcification of 

vertebrae 114 ; mandibular arch 

120; pectoral fins 130 
Hcythrops 42 ; interorbital septum 

333 
Sea leopard 48 ; see Ogmorhinus ; 

lion 48; manus 511 ; pes 526 ; 

position of limbs 29 ; otter 

48; pes 526 
Seal 369 ; manus 511 ; pes 526 ; 

sacral vertebrae 452 ; scapula 

497 



Secondaries, duck 303 f. 
Secretary-bird 41 ; claws 330 
Selachii 31 ; general characters 63 ; 

teeth 108 

Selenodont, defined 345, 428 
Sella turcica, crocodile 247 ; dog 

386 

Semionotidae 33 
Semiplumae 328 
Sense capsules, see Auditory, Nasal 

and Optic capsule 
Seps 38 ; limbs 289 
Shagreen 61 
Shaft of feather 302 
Shark 64; Frill-gilled 31; see 

Chlamydoselache ; Port Jackson 

32 ; see Cestracion 
Sheep 359 ; manus 507 ; teeth 345 
Shields of turtle 214 
Shin 26 ; see Cms 
Shoulder girdle, see Pectoral girdle 
Shrew 49, 370; auditory ossicles 

488 ; cervical vertebrae 446 ; pre- 

sternum 490; skull 481; teeth 

440 

Sigmpid notch, dog 406 
Siluridae 33 ; plates 105 
Simla 49; ribs 493; skull 484; 

thoraco-lumbar vertebrae 450 
Simiidae 49, 373 
Simplicidentata 47, 366 
Siphonops 35; 8. annulatus, skull 

178 
Siredon 35; skull '175; teeth 169; 

visceral arches 181 
Siren 35, 135, 188 ; beaks 168 ; 

branchial arches 180 ; digits 187 ; 

skull 174 ; teeth 169 
Sirenia 44, 522 ; arm bones 501 ; 

caudal vertebrae 453 ; cervical 

vertebrae 443 ; general characters 

352 ; hair 416 ; horny plates 418 ; 

manus 505 ; pectoral girdle 495 ; 

pelvis 514 ; ribs 491 ; skull 459 ; 

sternum 489 ; teeth 425 ; thoraco- 
lumbar vertebrae 448 
Sirenidae 35 
Sirenoidei 34; general characters 

70 

Xivatherium46; skull 469 
Skate 32 
Skeletogenous layer 14, 16; Amphi- 

oxus 52, 112 



INDEX. 



OOO 



Skeleton, defined 1 ; Cape Buffalo 
492; Ceratodu* 128: cod 83 f. ; 
crocodile 237 f. ; dog 374 f . ; duck 
302 f. ; frog 151 f. ; llama 496 ; 
newt 138 f. ; turtle 214 f. 

Skink 38; see Tiliqua 

Skull 16 f. ; Amphibia 173 f. ; Anura 
179 f.; birds 333 f.; cod 96 f . ; 
crocodile 243 f. ; diagram of 
Mammalian 385 ; Dipnoi 124 : 
dog 383 f. ; dogfish 73 f. ; donkey 
431 ; duck 312 f. ; fish 117; frog 
154 f., 159 ; Globicephalus 463 ; 
Gymnophiona 177 ; Indian ele- 
phant 474 ; Mammalia 455 ; 
Marsipobranchii 57; pig 466; 
Procavia 433; reptiles 276 f. ; 
Rhinoceros 421; Rhytina 46O; 
sloth 458 ; Tasmanian wolf 
456 ; Teleostei 124 ; turtle 222 f.; 
wombat 456 

Sloth 43, 352 ; auditory ossicles 
487 ; arm bones 500 ; claws 418 ; 
leg bones 517; manus 505; pec- 
toral girdle 495 ; pelvis 513 ; pes 
522 ; ribs 491 ; sacrum 452 ; skull 
457; sternum 489; teeth 424; 
thoraco-lumbar vertebrae 447 

Snake 38 ; see Ophidia 

Sole 33 

Solea 33 

Solenodon 49 ; teeth 440 

Solenodontidae 49 

Solitaire 42, 330 ; wing 338 ; wrist 
330 

Sorex 49; pelvis 515; see Shrew 

Soricidae 49 ; skull 481 

Spalacidae 47 

Spatularia 32; distribution 66 

Spelerpes 35 ; branchial arches 180 ; 
ribs 182 ; S. belli teeth 169 

Sperm whale 44, 357 ; see Physeter 

Sphargis 37 ; see Dermochelys 

Sphenethmoid, frog 156 

Sphenisci 40 ; see Penguins 

Sphenisciformes 40 

Sphenodon 37, 197 f. ; carpus 291 ; 
cervical vertebrae 275 ; fossae in 
skull 281; humerus 290; inter- 
parietal foramen 277; ribs 286; 
skull 282; tarsus 293-; teeth 
274 

Sphenodontidae 37 



Sphenoidal fissure, dog 388 

Sphenotic 20 ; cod 97 ; salmon 
89 

Spider monkey 49 ; see Ateles 

Spinacidae 32 

Spinal column 13 ; Dipnoi 113 ; 
fish 112; Holocephali 113; Mar- 
sipobranchii 56 

Spines, Elasmobranchs 61 ; mam- 
mals 417 

Spiny anteater 43; see Echidna: 
moused/; see Acanthomys 

Splenial 22 ; crocodile 258 ; duck 
320 ; turtle 231 

Spurs, birds 330 ; Monotremata 
418 

Spur- winged goose 330; plover 
330 

Squalidae 31, 64 

Squalodon 45,357; dental formula 
427 

Squalodontidae 45 

Squamata 37; general characters 
198 ; position of teeth 272 ; skull 
278 

Squamosal 21 ; crocodile 256 ; dog 
394; duck 316; frog 160; newt 
144 ; turtle 229 

Sqnatina 32; calcification of ver- 
tebrae 114; labial cartilages 119; 
tail 63; vertebral column 114 

Squatinidae 32 

Squirrels, frontals 476 ; pes 526 

Stapes, dog 393 ; frog 157 ; man, 
dog, rabbit 485 ; newt 141 

Steganopodes 41 

Stegosauria 39 ; general characters 
209 

Stegosauridae 39 

Stegosauruz 39, 208 f. ; exoskeleton 
272 

Steller's sea-cow 44 ; see Rhytina 

Stereornithes 41 

Stereospondyli 35 

Sternal ribs, crocodile 259 ; dog 

402 ; duck 320 ; mammals 490 f. 
Sternebra, dog 404 

Sternum 24 ; Amphibia 182 ; birds 
336; crocodile 260, 261; dog 

403 ; duck 321 ; frog 163 ; 
Mammalia 489 ; newt 145 ; rep- 
tiles 287 

Stork 335 ; White 41 



556 



INDEX. 



Striges 42 ; see Owls 

Stringops 42 ; sternum 336 

Struthio 40, 299 ; see Ostrich 

Struthiornithes 40, 299 

Sturgeon 32 ; see Aclpenser 

Stylo-hyal, dog 399 

Suborbital bar, duck 318 ; ridge, 

dogfish 76 

Subplantigrade, defined 358 n. 
Subungulata 46 ; arm bones 502 ; 

general characters 360 ; manus 

509; pelvis 514; pes525; shoulder 

girdle 497 ; skull 471 ; teeth 432 ; 

thigh and shin 519 
Suidae 45 
Suina 45, 358 f. ; fibula 519 ; manus 

507; odontoid process 445 ; pelvis 

514 ; pes 523 ; ulna 501 
Sula 41 ; see Gannet 
Supinator ridge, dog 406 
Supine position, defined 29 
Supra-angular 22 ; crocodile 258 ; 

duck 319 ; turtle 230 f. 
Supracaudal shield, turtle 214 
Supraclavicle, cod 102 
Supra- occipital 19; crocodile 247; 

dog 386 ; duck 315 ; turtle 224 
Supra-orbital 20 ; crocodile 251 
Suprapharyngeal bone, cod 101 
Suprascapula, crocodile 263 ; frog 

162 
Supraternporal arcade, crocodile 

256 ; reptiles 281 
Surinam toad 36 ', see Pipa 
Sus 45; dental formula 428; see 

Pig 

Suspensorium, Amphibia 173; dog- 
fish 78 ; duck 319 ; frog 160 ; newt 
144 ; Pisces 61 

Sutures 12 

Swan 41; cervical and thoracic 
vertebrae 332 

Swift 42, 335 ; foot 342 

Symplectic, cod 100; salmon 94 

Tails, fish 60 

Talpa 49; pelvis 515; see Mole 

Talpidae 49 

Tapir 46, 360; malleus 487; pes 

524, 525 ; teeth 345 ; see Tapirus 
Tapiridae 46 ; dental formula 429 
Tapirus 46 ; fibula 519 ; manus 

5O8 ; skull 471 ; see Tapir 



Tarsier 49 

Tarsiidae 49 

Tarsipes 43, 349'; mandible 457 

Tarsius, 49, 372 ; pes 527 

Tarso-metatarsus, duck 327 

Tarsus 26 f. ; crocodile 268; dog 
414; frog 166; newt 150; turtle 
236 

Tasmanian devil, 43; see Sarco- 
philus; wolf 43; see Thylacinus 

Tatusia 44 ; stapes 487 ; teeth 424 

Tectospondyli 114 

Tectrices, duck 306 

Teeth 6 ; Amphibia 169 ; birds 330; 
cod 83; crocodile 238; develop- 
ment 7; dog 374 f.; fish 106f.; 
frog 158 f. ; horses 5 ; mammals 
344, 420 f. ; pharyngeal 8 ; rep- 
tiles 272 f. ; structure 4 ; succes- 
sion 7 

Teleosauridae 39 

Teleosaurus 39 ; palate 281; scutes 
271 ; vertebrae 275 

Teleostei 33; general characters 
69; ribs 126; skull 124; tail 
117 ; teeth 110 ; vertebral column 
115 

Temnospondyli 35 

Tenrec 49; see Centetes 

Tentorium, dog 392 

Terrapin 37 

Testudo 37, 194 

Tetraceros 46; horns 417 

Thalaxitochelys, carapace 216 

Thecodont, defined 273 

Theriodontia 36 

Theromorpha 36; general charac- 
ters 191; humerus 290; pectoral 
girdle 288; ribs 285; skull 278; 
teeth 273 ; vertebral column 275 f . 

Theropoda 38; general characters 
207 ; teeth 273 

Thoracic ribs, crocodile 259; see 
Kibs ; vertebrae 16 ; crocodile 
241, 242; dog 381, 382; duck 
310 ; turtle 221 

Thoraco- lumbar vertebrae, mam- 
mals 447 f. 

Thornback skate 104 

Thylacinus 43; atlas 443; dental 
formula 423; pelvis 513; pes 
521; skull 456 

Thijlacoleo 43; skull 457 



INDEX. 



557 



Thyro-hyal, dog 399 

Tibia 26; crocodile 268; dog 412; 

newt 149: turtle 235 
Tibiale 27 ; see Tarsus 
Tibio-fibula, frog 166 
Tibio-tarsus, duck 326 
Tichorhine Rhinoceros 470 
Tiger 48 

Tiliqua 38; scutes 200, 271 
Tillodontia 47, 365; femur 520; 

manus 511 ; teeth 435 
Tinamidae 300; caudal vertebrae 

333 ; vomers 334 
Tinamiformes 41 
Tiiiamus 41; ischia 341 
Titanotheriidae 46; skull 170; teeth 

432 
Titanotherium 46; humerus 501; 

manus 508 ; pes 525 
Toad 36 ; shoulder girdle 1*5 
Tope 32 

Torpedinidae 32 
Torpedo 32, 104 

Tortoise 37; position of limbs 28 
Tortrix, ischio-pubis 292; traces 

of posterior lirnb 293 
Toucan 42; foot 342 
Toxodon 46, 361; femur 519; pes 

525 ; teeth 432 
Toxodontia 46; general characters 

361 ; manus 509; skull 472 ; teeth 

432 

Tosodontidae 46 
Trabeculae 11; cranii 17 
Tragnlidae 46 
Tragulina 45, 359; fibula 519; 

manus 507 ; odontoid process 

445 ; pes 523 ; skull 468 ; teeth 

4-_ ) ',t ; ulna 501 

Transpalatine, crocodile 255 ; rep- 
tiles 278 

Trapezium 27 ; dog 408 
Trapezoid 27 ; dog 408 
Trichechidae, 48, 369 
Trichechu* 4S; see Walrus 
Trionychia 37 ; general characters 

194 

Trionychidae 37 
Trionyx 37, 193 f. ; exoskeleton 

214, 270; skull 283; vestiges of 

teeth 274 

Trissolepis 32; scales 104 
Tritylodon 43 ; teeth 348 



Trochanter, dog 412 ; duck 326 

Trochilidae 42 ;*see Humming-birds 

Trochlea, crocodile 263 ; dog 405 f.; 
duck 323; turtle 232 

Trogon, 42 ; foot 342 

Trogonidae 42 

Tropidonotus 38; jaws 280; skull 
279 

Trunk vertebrae, cod 84; see tho- 
racic and lumbar vertebrae 

Trygon 32; calcification of verte- 
brae 114; caudal spine 106 

Trygonidae 32 

Tuberosities of humerus, dog 405 ; 
of ischium, dog 411 

Tunicata 30, 51 

Tupaia, skull 480; thoraco-lumbar 
vertebrae 450 

Turbinals, dog 395 

Tursiops 45 ; skull 462 

Turtle 37; anterior limb 232, 234 ; 
cranium 222 f.. 226 ; hyoid 231, 
285; mandible 230; pectoral 
girdle 231; pelvic girdle 235; 
pes 236; plastron 217, 218; pos- 
terior limb 234. 235; sense cap- 
sules 227; skull 222; vertebral 
column 219 ; Leathery , see 
Dermochelys ; Snapping , see 
Trionyx 

Tylopoda 45, 359 ; fibula 519 ; ma- 
nus 507 ; odontoid process 445 ; 
pelvis 514; pes 523; skull 468; 
teeth 428; ulna 502 

Tympanic, dog 392 ; cavity, 
crocodile 250; diagram of mam- 
malian 391; dog 393; duck 
315 f.; turtle 228; recess, 
duck 315 

Tympano-hyal, dog 399 

Typhlopidae 38; scales 270; skull 
*278 

Typhlops 38; ischio-pubis 292; 
traces of posterior limb 293 

Typotheriidae 46 

Typotherium 46, 358, 361; clavicle 
495, 497; femur 519; pes 525; 
skull 472 ; teeth 432 

Udenodoti 36, 192; beak 271 
Uintatheriidae 47; skull 364 
Uintathcrium 47; dental formula 
433; leg 519; limbs and limb 



558 



INDEX. 



girdles 516; manus 510; pelvis 

514; skull 473 
Ulna 26; crocodile 265; dog 406; 

duck 323; frog 164; newt 147; 

turtle 233 

Ulnare 27; see Carpus 
Umbilicus, inferior and superior, 

duck 303 
Unciuate process 190; crocodile 259; 

duck 320 

Unciform 27, 345, 504 ; dog 408 
Ungulata 45 ; auditory ossicles 487 ; 

caudal vertebrae 453; cervical 

vertebrae 445 ; general characters 

357 ; manus 506 ; pectoral girdle 

495; pes 522; ribs 491; sacrum 

452; skull 464 f.; sternum 489; 

teeth 427 f. ; thoraco-lumbar ver- 
tebrae 448 
Ungulata vera 45 ; arm bones 501 ; 

general characters 358; manus 

506; pelvis 514; thigh and shin 

519 
Upper arm 26 ; crocodile 263 ; dog 

405; duck 323; frog 164; newt 

147 ; turtle 232 
Upupa 42 ; see Hoopoe 
Urochordata 30, 51 
Urodela 35; general characters 

134; pelvis 187; ribs 182; skull 

174 

Urohyal, cod 101 ; duck 320 
Urostyle, Anura 172; cod 85; frog 

153 ; Teleostei 117 
Ursidae 48 ; humerus 502 
Ursus 48 ; dental formula 439 ; see 

Bears 

Vacuities, anterior palatine , cro- 
codile 252, 258 ; in reptilian 
skull 281 ; posterior palatine , 
crocodile 254, 257; pre-orbital 
, reptiles 283 f. 

Vampire 49; teeth 441 

Vane, of feather 303 

Varanidae 38 

Varanus 38; shoulder girdle 2O2 ; 
skull 20 1 

Vasodentine 108, 272 

Vertebral column 14; Amphibia 
170; birds 332; cod 83; croco- 
dile 239; dog 378; duck 307; 
Elasmobranchs 113; frog 152; 



mammals 442 ; newt 138 ; turtle 

219 ; - ribs, crocodile 259 ; dog 

402; duck 320; shield, turtle 

214 

Vertebrata, general characters 53 
Vexillum, of feather 303 
Vibrissae, dog 374 
Viscacha 47 
Visceral skeleton 21; dogfish 77; 

Elasmobranchs 119 f. 
Viverra 48; acetabular bone 515 
Viverridae 48 
Vomer 21 ; cod 98 ; crocodile 252 ; 

dog 395; duck 317; frog 158; 

salmon 93 ; turtle 229 
Vomero-palatine, newt 143 
Vultur 41 
Vulture 41 ; Black , shoulder 

girdle and sternum 337 

Waders 335 

Walrus 48, 367, 369; canines 420; 
manus 511; pes 526; position 
of limbs 29; skull 480; teeth 
440 

Warblers 42 

Wart hog 45; teeth 428 

Weasel 369 

Whale, baleen 3, 418; Ca'ing - 
45, see Globicephalus ; Hump- 
backed 44, 357 ; Eight 44, 
357 ; Sperm 44, 357, see Phy- 
seter; True or Whalebone 356 

Whiting 33' 

Wild duck 41 ; see Duck 

Wing, duck 322 ; Gannet, Ostrich, 
and Penguin 339 

Wolf 48 

Wombat 43; atlas 443; pes 521; 
sacrum 451; skull 456; tail 
453 ; teeth 423 

Woodpecker 42, 335; foot 342; 
hyoid 336 

Wrasse 33; teeth 111 

Xenacanthus 31; pectoral fins 130 

Xenopidae 36 

Xenopus 36; branchial arches 182 ; 

nails 168 ; pelvis 188 ; ribs 182 
Xiphiplastron, turtle 217 
Xiphisternal horn, crocodile 260 
Xiphisternum, dog 404 ; frog 163 
Xiphoid process, duck 321 



INDEX. 559 

Zeugladon 44, 353, 356; dental 240 f.; dog 379 f.; duck 308 f.; 

formula 426; dermal plates 420 frog 152 f. ; newt 139; turtle 

Zeuglodontidae 44 219 f. 

Zvgantra, denned 199 n. ; reptiles Zygosphene, denned 199 n.; reptiles 

"276 27i5 
Zygapophyses, cod 84; crocodile 



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